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Big boobs that look great, but when said female lays on her back, her boobs sag off of her chest into the axilla.

Instead of a steep canyon of excellent cleavage, armpit tits will slope off the chest and resemble small rolling hills.

Excessive sternum
"Bro, That chick last night night was wild, but found out she had armpit tits when we went back to her place!"
by longnights51 January 21, 2012