Things I probably knew but preferred not to think about

Bounce

2. To engage in sexual intercourse; prob.: from the expression ‘bouncing the mattress’, but influenced by Roo's psychosexually loaded “Try bouncing me, Tigger!” from the Winnie-the-Pooh books.

Ye great gods and little fishies. I'll never read 'Pooh' in quite the same way.

Via.