score:4
German passport holders are visa exempt for stays in Thailand up to 30 days.
You can catch a train from the airport to the city centre, with the trip taking ~20 minutes and cost 150 baht the last time I was there.
Given the above two facts, you could very easily head into central bangkok for the day - once you are out of the airport, the city is your oyster, enjoy some street food, grab a beer on a rooftop bar, visit a museum, take a water taxi etc. You can even go and find a cheap hotel somewhere outside the airport if you like, but assuming your final destination is in South East Asia, you are probably better off fighting through the need to sleep and enjoying your day of exploring.