The leaning tower of pisa is a sexual position in which 2 men and two women are involved. Each man is in the doggy style position with their woman, side by side and then perform a high five which creates the leaning effect of the tower.
Michael:"Hey Will that hoe is totally down for a leaning tower of pisa if yo girl Leilah is!"
Will:" Is that the one where we both fuck them and then high five?! ooohhh man im totally down!!!"