Hey, santaclause! Bellybutton piercing on guys is kinda questionable thing. I want bellybutton piercing too (and I am also 100% straight), but i think that barbells and dangly bellyrings doesn't look good on a man's navel. But it's only my opinion and if you think you will look good with dangly piercing - go on and just do it)
IMHO, bellybutton piercing on guy would be look cool if he has an athletic body and a small captivate bead ring or so-called circular (horseshoe-shaped barbell) in a navel. Or it must be non-standart piercing like true navel piercing, or another unusual placement.
P. S. Sorry for my English.
Credits, Irwin.