Went to washroom. washed hands. came back drank my beer. found what looks like a pubic hair in my mouth. could i get an std from this hair?

Not likely: But beware, if you are in a public place, you should never leave your beverage unattended, rather you ought to carry it with you. It is way too easy for someone to "slip you a mickey." since ou likely can't take it outside (e.g. To join a friend who smokes), finish your drink first or get a new one when you return.

Highly unlikely: Stds require contact of mucosa to mucosa, or fluid to mucosa; it is highly unlikely that a pubic hair, in beer, would be able to transmit any std to you.