"I'll bet you my penis can't fit inside your vagina. If you win, you get to have sex with me!"
"Pardon me, but could I interest you in some orgasms?"
"It's not long, but it's skinny!" (warning: highly risky)
"You remind me of a girl I used to know who loved having casual sex with me"
"Do you have any (your ethnicity) in you? Want some in your vagina?"
"Whooo, baby, you're making MY 'seventh inning' stretch!" (only effective during the seventh inning at baseball games, if at all)
"What are you, chicken?"