When your penis gets goose bumps and send shivers in that area Also adding a tingling feel.
David: shit my penis is tingling
Mark: damn you got penis tingles too?
A phenomenon one gets when a stock contained in the Zack Morris Index begins to climb as stated by @MrZackMorris himself. One does not have to see it happening to experience the Tingle.
I experienced a penis tingle when $STRN went to $15 today. I stopped working out and checked my account to find that my balance had doubled. Zack called it yet again.