If you see a particularly good looking person, with pecks and abs and six pack etcetc. then you can call them 'sex on legs'. They give joy to your eyes, and, in this way link to sex. Just not in bed, but on legs.
Alice: WHOA, LOOK AT THAT FINE PIECE OF sex on legs.
nickname given to American Idol2006 winner Taylor Hicks because of his ability to make women go through entire packs of panties just by looking at them sideways or playing with his harp.