What to do if i hit my nose against a muscular guy?

Apologize: As you would if you were to do something clumsy with anyone else. I have known quite a few bodybuilders, and while most of them are even-tempered and actually very secure because of their strength, some of them are short-tempered, especially about touch. If the time for apology is past, don't worry. Infection is unlikely to be transmitted in this way.