Leah reckons if Mack and Michael were put in a blender, they'd be the combination of her perfect man. Bloody and dead, I guess. Leah also tells Mack that if she got a date card, she'd take Michael on the date. Mack is confused because he thought Leah was into him. Leah says she doesn't want to regret her time in paradise by spending it all with Mack. Are you keeping up? OK, as all you metalheads say, here's the breakdown.
Basically Leah is saying she doesn’t want to bonk Mack yet, because she’s not sure if someone better will come along, and if she bonks Mack now, she’ll regret it later if someone better DOES come along. Mack is her safe second choice and if no one better comes along that she's actually sexually attracted to, then she’s excited to have Mack as a backup plan.