How to tolerate if someone insulting Buddhism?

Buddhists don't do nothing do they? Cultivate compassion and Metta for them instead of anger like they are cultivating anger or ignorance and you will be doing something as a good person :)

So an example from another faith. I met a gentleman by the name of Ron. He was from Barbados and had moved to the US for better opportunity. Back when he lived in his homeland, Ron had been a doctor. Before he could practice medicine in America, Ron had to recertify in a number of areas (I remember him complaining about hematology the most!) I was working at a bookstore at the time and everyday, he'd come to our cafe to study.

Now Ron was a well dressed chap and nice as any person you'd ever want to meet. Everyday he'd come and talk to me and the other staff members for a bit. He had a great sense of humor and always had a kind word for everyone. Ron used to spend a lot of time talking to me because I was a competitive weight lifter at the time. Ron had been Mr. Barbados back when he was younger, so we had a lot to talk about. I even used to even call him after my weight lifting meets to tell him how I did. Whenever I placed, I swear he was happier for me than I was. You could not love this man!

Ron studied at our store for about a year. Right before he went off to take his medical boards, he joked about how he had to present all kinds of ID as a security measure against cheating. "Cheating!" he says to me. "I'm a Jehovah's Witness! We don't cheat!" Now, I don't know if you know anything about Jehovah's Witnesses, but a prime tenant of there faith is to spread it. Where I live, they'll even go door to door proselytizing. They call it "bearing witness" Ron never did any of that. In fact, it was such a departure from what I was used to, I asked him how after a year, he never spoke a word about his religion. I'll never forget his words.

"To convince someone with words is cheap. The mind is not the place of faith. My whole life is my witness for others."

The only way you are going to convince anyone of the efficacy of the dharma is in how you conduct yourself. It's a waste of effort to try and argue with someone else about Buddhism. You aren't going to convince them. The only thing that is going to change their minds are your actions of body, speech, and mind.

Just don't get attached to Buddhism

Example :

In school , if a teacher scolded you , you get really upset and humiliated, but that does not happen if your teacher scolded someone you don't know . Let's ask why , because you are attached to yourself and not to a some person who you don't know. This applies to everything. If you take something as yours , you will make a bond with it, thus all the sadness and anger will come along eventually because of that bond you made. So if you take Buddhism as your religion, the best religion(we all know it is the best ) and try to make attachments with it, you will be sad and angry if someone insulted it.

Religions can make terrorists

Yes above statement is true. We have seen on news , people becoming terrorists because of some religions. Basically it happens when someone doesn't know what that religion really taught , but when trying to make bonds with it. So those people think the only religion in the world is their religion.

Conclusion

We should not make attachments with anything. At least we should try not to. When following the path to nirvana, you have to give up everything, if you gave everything up and still stuck without achieving nirvana, that's the time you should give up the desire to achieve nirvana. Then only you can achieve nirvana. It is a very complex point, think about it more.

But at the time when someone insulting Buddhism what to do ?

I think you're supposed to remember that people are heir to their own karma.

If people insult Buddhism instead of respecting and learning from it, instead of benefiting from it, then you might feel pity for them (or preferably compassion).

I'm not sure you or I should see a need for forgiveness (i.e. a need for us to forgive them) because I (hypothetically) don't see their disrespect as hurtful towards "you" or "me". Perhaps you're identifying with Buddhism in some way (thinking that their disrespect is hurts others or hurts you, and needs forgiveness)?

I get really really angry.

See for example the Dhammapada, which begins with,

3. "He abused me, he struck me, he overpowered me, he robbed me." Those who harbor such thoughts do not still their hatred.

4. "He abused me, he struck me, he overpowered me, he robbed me." Those who do not harbor such thoughts still their hatred.

5. Hatred is never appeased by hatred in this world. By non-hatred alone is hatred appeased. This is a law eternal.

6. There are those who do not realize that one day we all must die. But those who do realize this settle their quarrels.

Getting really angry doesn't seem to me appropriate. I think of replying with anger as being like "putting out fire with gasoline", i.e. it may fuel disrespect and further anger, rather than putting it out.

I realize many people feel that they shouldn't usually get angry, but might feel that sometimes anger is excusable, normal, necessary, even praise-worthy, and inevitable (e.g. "if I get angry that their fault for being disrespectful, not my fault"); for example:

• I don't usually get angry; but if you insult my mother then I'll punch you!
• I wouldn't usually fight; if you attack my country then of course I will!
• I'm usually a nice guy; but if you attack my religion then I can't stand it!

I also realize that some countries/societies criminalize disrespect, which might make it see normal to try to punish disrespect (e.g. by meeting it with anger), and/or to be averse to (and unaccustomed to) disrespect.

But ignoring what society does and looking at the scripture, remember the parable of the saw:

Monks, even if bandits were to carve you up savagely, limb by limb, with a two-handled saw, he among you who let his heart get angered even at that would not be doing my bidding. Even then you should train yourselves: 'Our minds will be unaffected and we will say no evil words. We will remain sympathetic, with a mind of good will, and with no inner hate. We will keep pervading these people with an awareness imbued with good will and, beginning with them, we will keep pervading the all-encompassing world with an awareness imbued with good will — abundant, expansive, immeasurable, free from hostility, free from ill will.' That's how you should train yourselves.

because of the silence of the good people

If you think it might help, maybe you can disagree without getting angry.

If someone tells a lie about Buddhism, for example, maybe you can say what the truth is; or if it's not an appropriate place and time for a lecture, maybe say something short like "I disagree" or "I don't think so" ... enough so that if someone is interested then they can ask for more.

The world suffers a lot. Not because the violence of bad people. But because of the silence of the good people.

I think that Buddhism teaches that causes of suffering are ignorance, craving and attachment and so on.