Sex with your boss, professor, or another person you have no business fooling around with . . .
"I did not have sexual relations with that woman . . . it was just 13th base!" -- Bill Clinton
by Scylla June 28, 2006
having sexual intercourese with your partner while wearing Sherlock Holmes hats, smoking pipes and completing a crossword in under 10 minutes.
I got to 13th Base with the wife yesterday and she came allover my deer stalker
by sergio97 January 01, 2011
Having sex while messing around with unlucky things. Caution is advised. May result in unpleasant results.
Man, I went to 13th base in the house of mirrors under a ladder while a black cat opened an umbrella indoors and crossed between me and her (it joined in for a bit of course) last Friday the 13th and MAN was it great!
by TriedTooManyBases October 22, 2011
When you have sex with an animal and a person at the same time.
"Dude, that weird dude next door got to 13th base last night."
by Mr. Supotco November 13, 2015
(male) when you have intercourse with a female and you end up getting warts, aids, and every other STd you can think of.
Man this girl took me to 13th base and now my life is over!
by Will Deshazo June 04, 2006