Bestfriend's Bump.

Cassidy and Tyler have been bestfriends for ages; no, not since kindergarten, but since they were born, their mothers are bestfriends so in turn so are they.
Cassidy and Tyler both go to a party, Cassidy for beer pong and Tyler for some free drinks; Cass wins some money after betting and winning so they both decide to get ice cream and candy as their prizes.
They both go to Tyler's slightly tipsy and fully excited.
One thing leads to another and they end up sleeping together.
And, uh-oh, Cassidy ends up pregnant with her Bestfriend's Bump.

(Not really a good description, but whatever, just read please!)