Adults use it as a colloquialism - referring to events that we probably should’ve experienced earlier in life (i.e, as a baby’s first) but instead are experiencing it for the first time as an adult.
Adult 1: You've never been to a concert?
Adult 2: No! Crazy, right?
Adult 1: awww baby's first concert!
by Hay_Hay_Hay October 25, 2019
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The moment during vaginal childbirth when the baby's head first emerges from the vulva resulting in a "Collar-O-Giner"!

The vagina forms a collar-like apparatus.
"Nowadays it is fashionable for baby's first turtleneck to be suede-like but during the 70's, the style was Angora!"
by GOFS February 04, 2010
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also known as FBDS, the guy you screwed around with and had a baby with for the first time, mostly affects young girls from ages 14-19 years old who have kids extremely young and before marriage.
Lindsay: I really might get back with my ex
Bobby: why he's a total douche to you and doesnt even care about lil jonny
Lindsay: because he's my first baby daddy!
Bobby: ah! fuck girl you've got a case of First Baby Daddy Syndrome!
by sexymilfmomma February 23, 2012
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When you're banging a pregnant girl on Sunday and finish inside giving the baby a white treat for the first time
Man I'm going to hell for giving a girl a babys first icecream Sunday
by AchieverD January 13, 2016
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