Hey! I just premiered a boy Pinkie Pie costume this past weekend at AM2 in Anaheim!
Warning, though-- I didn't cut back on the cuteness and frills, so my variation (while guyish) still isn't for the faint of heart. It's easily adaptable into a more socially-comfortable outfit, though, if you trade the fluff for denim or jogger's pants.
An alternate option I enjoy sometimes is mixing a pair of standard guys' athletic shorts with a pair of colored tights under them. Gives you a dash of pop and color while sticking to a sporty male look.