Depending on what aspect of Pinkie's personality you're going on, I could see a lot of things working.
I am personally fond of the frat-boy or preppy Pinkie Pie described above. It's simple, but could be quite recognizable. And it isn't that unusual for guys to wear pink right now. The raspberry jeans that were mentioned may be available at Target, actually, in that retina burning pink shade. I know I've seen a pair of bright pink mens shorts that I thought would work pretty well for a Pinkie Pie outfit. You could even do a hipster Pinkamena (with the straight hair hanging over one eye, ala when she goes crazy(er))
I've been working on hunting down pieces for a female Pinkie Pie Cosplay that could likely work on anyone, with some changes. Raver/Club Pinkie Pie. Pale Pink parachute pants, with the Cutie Mark painted or embroidered on the pockets. A neon pink fishnet shirt under a pink t-shirt with the Cutie mark, again. Possibly yellow, pink, and blue necklaces and bracelets to match. Short spiky or curly hair could work, too, I think.
We're actually working on what is turning out to be a bit of a D&D group of MLP:FIM, which includes 3 male versions (Rarity, Twilight Sparkle, and Rainbow Dash) in various styles. Twilight Sparkle is going to be done up as a wizard or monk, Rainbow Dash as a fighter or rogue, and Rarity is honestly the hardest... leaning currently towards a really fancy looking Bard, actually.
Can't wait to see how this turns out.
Party Pirate Pinkie Pie (MLP:FiM) 100%
Eris Discordia (MLP:FiM) 100%
Convention Line-Up: BronyCon 2013 - Dragon*Con 2013
Eris (Female Discord, MLP:FiM), Casual Gala Pinkie Pie (MLP:FiM)
The 10th Doctor, blue suit variation (DW), Queen Mab's Party Dress (Dresden Files: Cold Days), Party Pirate Pinke Pie