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1.
When a girl rests her boobs on top of your head, like a hat.
Jen just came over and gave me a Boobie Hat.
by Wearer of the Boobie Hat July 27, 2009
 
2.
Most types of breast support, specifically the cup-style bra. Also includes the bikini and similar articles of swimwear or undergarments.
Does not including the sports bra, t-shirt bra or other full coverage, non-cup styles.
She took the twins shopping for boobie hats this afternoon.
by gwally February 04, 2012