noun, plural -sies, verb, -sied, -sy·ing.
When a Manly man imagines; usually extravagantly and over exaggerated, about doing something of a erotic/funny nature to another man. Can also be used for awesome ideas that guys would love to actually do, but will prob never happen.
Usually the men are already involved in bromantic activities together.
Guy 2: Yeah, this is a mantasy come true!
Guy 1: Suck it!
Guy 2: Only in your mantasies.
While performing a mantasy, Emily became angered when Dave rested his xbox controller on top of her head.