Need tips on fighting?

So i might have to fight a guy in case he starts getting in my face at a canada day party i am attending this game is much older than me like 5 years but is the same height as me but more built not roid huge but toned and kind cut i am skinny but i workout allot on pull up bar would a a nice punch to the nuts be cheap of me or necessary anyways hes older why not fuking asshole :( (o yeah i got longer arms 2_