Mumangoes can be used to describe mammoth mammaries. It kinda attempts to fuse magnanimous, used in its meaning of generosity, and mangoes, a well-known term for boobs. So a generous helping of mangoes, ie a pair of massive mammaries, can simply be called Mumangoes.
A: Dude did you see the Two and a half men epi last night?
B: Yeah man... That new chick got introduced, Chelsea!
A: Fuck yeah man did you see those mumangoes? They're fucking ridick!
When ur friends are being uber cheap on a night out, especially when it's out of character. So much so that u start to think that this person's not somebody u know. Hence, an imposter. So to fuse cheap and imposter....
A: Bro I only got like 5 bucks on me. Can you pay the rest of it for the taxi ride?
B: You Fucking Cheaposter!