A late-Eighties coining, to pun on bimbo, it had an air-head connotation at first but now means one who can flex his abs without getting sand kicked in his face. Bimbo dates from 1920 (a decade before the first OED citation), when it meant a sluttish woman and also - as it still does in America - a stupid man. When called a bimbo on the Donohue show, Dan Quayle had not mooted a sex-change - but doubtless would if there were votes in it.
IN Q magazine, Mel C is sassier than in the collective vacuity of the popular sing-ing combo, the Spice Girls. She parries questions about her ever-thwarted love-life, such as a dalliance with a himbo Kavana, a hunk. It is not in the OED, nor the "world English" of Encarta, which goes directly from himation to Himmler.