Obligation-free sex which happens on or around someone's birthday. Usually initiated by the birthday boy/girl's partner, and involving a mix of acts which more favour the birthday boy/girl's preferences.

The usual rules of reciprocation and mutual pleasure are temporarily suspended, and the birthday girl/boy is considered free to cum whenever and wherever the fuck they please.
Nah, can't come out tonight... I'm hoping for birthday sex.
by evilbrent September 19, 2006
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having sex to celebrate your parents having sex
Guy:"do you want to have birthday sex?"
Girl:"you celebrating my parents having sex"
by calmyourtiddies March 03, 2020
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the best kind of sex and the best present ever. when your girlfriend/ boyfriend/ wife/ husband/ fiance/ your one night stand has sexual intercourse with you on your birthday
baby for my birthday this year I'd love to have birthday sex with you.

what are you doing on your birthday? sorry the mrs is coming over to give birthday sex
by smoked fish February 17, 2017
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its when you get some sucky or some fucky for your birthday, with no relationship needed
he got her poosy for his birthday, and theyre just friends
by jhjsahdsa October 23, 2004
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A Miller Lite, Bud Light, or other light beer served in a bottle with one sip replaced with a shot or half shot of vanilla flavored vodka (Svedka, Smirnoff, Stoli, etc.) Put your thumb on the top and gently flip the bottle over to mix. Tastes like cupcakes.
how'd you get so fucked up on just bud light?

i was actually drinking birthday sex.
by brokedownman July 19, 2010
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its THAT shit. birthday presents riii ahhhh iiiii de OUT
Liz got dat birthday sex when midnight hit.
by Sir Cott August 24, 2009
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the best birthday present. Usually involving 1 or more hookers.
My mom got me the birthday sex and I was satisfied. I always anticipate my birthdays in the future hoping for this present.
by niccos May 12, 2008
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