The Handshake Dilema

When someone offers that slightly raised open palm to one side, am I supposed to know which handshake to give? Is it the slap-wipe-and-punch combo? Or the thumbs crossed grab and shake (with optional light finger brushing)? Or the traditional firm shake with optional curled finger tug or finger tug and punch combo finish? I’ve had a few of those slap-punch combos but I was unsure whether it’s supposed to be a slap or a grab (and whether the thumbs should be crossed or not) so I’ve been doing a hesitant, in between variation of these to cover all the bases. And I keep forgetting that third punch and leave him hangin’. I never had to worry about this stuff in elementary school. Or even high school. I think I started shaking hands in college.