Derived from the saying "Why eat Spam, when you have Steak at Home". Spam being the lowest form of meat, while steak represents a worthwhile meal. Refers to a man that cheats on his hot wife or girlfriend with an undesirable, disfigured, or otherwise deformed ugly.
"She should leave him. She's always slaving at home while he's out Poundin' Spam".
"She's so hot, I don't know why he's always Poundin' Spam."
"Girl are you Trippin' Vag? You shouldn't be Poundin' Spam in the house, Tim is on his way home."
"Tim, did you really pound that spam for packs of free gum?"