I'd tattoo the kind of flower Manny gives off, when he got shot, on my chest right were Manny had it. Though the problem is I am quite the hairy fellow, so I'd probably put it where my chest meets my shoulder, there's not much hair there.
Or you could tattoo Manny's cyndrical head onto the side of your shoulder. If you were really ambitous you could tattoo the whole mural, the one you see when you save your game, on your back, or maybe just the title of the game in GF font.
I'd like to see of what and where other people would tattoo GF stuff on their body.