In Buddhism can all we percieve / experience b used as teachers?

A trite answer might be "Yes, everything is a learning experience! You can learn from anything".

A better answer might be "No: maybe not".

• To start with, saying for example that "a turnip can be used as a teacher" maybe does a disservice to actual/genuine teachers (including the Buddha himself).

• The Bhikkhuni Sutta suggests that various things like food, and even craving and conceit, can be helpful or instrumental. But not sexual intercourse, it says. It doesn't explain why, but perhaps we might infer that sexual intercourse cannot be "used as our teacher".

  Although I note that perhaps some forms of Buddhism do teach that, in some circumstances and for some people, there is something to be learned from sexual intercourse.

• I suspect that maybe negative emotions, such as anger or jealousy, maybe can't be used as a teacher. Maybe they teach remorse ... however the lesson you ought to be learning instead of that is "skillful virtues" and "freedom from remorse".

  You say that anger "protects the person's personality, so it's possible to say anger is a friend then". I suspect however that if you practice anger, then that does nothing but teach you how to be angry (which maybe isn't a lesson worth learning, nor a "personality" you want to preserve).

Anger certainly exists in lower beings such birds, goats, dogs, etc. That is why, in Buddhism, anger does not represent the 'human state' ('manussa-dhamma'). Instead, in represents 'birth' ('jati') in the 'animal world' (tiracchā­na­yoni).

Sensual desire... ill-will (anger)... sloth & drowsiness... restlessness & anxiety... uncertainty is an obstacle, a hindrance that overwhelms the mind and weakens wisdom... when a monk has not abandoned these five obstacles... for him to understand what is for his own benefit, to understand what is for the benefit of others, to understand what is for the benefit of both, to realize a superior human (manussa) state (dhammā), a truly noble distinction in knowledge & vision: that is impossible.

Avarana Sutta

Although anger is certainly a pre-programmed instinctual survival mechanism, does anger teach us it is the ideal way to respond to perceived threats? Or is there a more 'human' ('reflective/wise') way to respond to perceived threats?

Buddhism explains everything can be a teacher, it that everything has:

(i) a cause/reason for its arising (samudaya);

(ii) a condition for its passing (atthaṅgama);

(iii) an attractive, alluring or stimulating quality (assāda);

(iv) a danger or drawback (ādīnava);

(v) a method to escape from the danger (nissaraṇa).

When people confessed their sins (moral transgressions) to the Buddha, he generally responded their sins were a 'teacher' for their growth & development. For example:

Yes, great king, a transgression overcame you in that you were so foolish, so muddle-headed, and so unskilled as to kill your father — a righteous man, a righteous king — for the sake of sovereign rulership. But because you see your transgression as such and make amends in accordance with the Dhamma, we accept your confession. For it is a cause of growth in the Dhamma & Discipline of the noble ones when, seeing a transgression as such, one makes amends in accordance with the Dhamma and exercises restraint in the future.

DN 2

The Buddha told us the three marks of existence, all things which exist in the mind have these properties:

Sabbe sankhara anicca

Sabbe sankhara dukkha

Sabbe dhamma anatta

All conditioned things are impermanent, All conditioned things are suffering, All things are without a self.

This means that everything has the potential to teach us. We can learn about impermanence, dukkha, and not-self from anything which arises in the mind.