I doubt the pros would be called out for whatever they wear. Ronnie has gotten away with flipping the backs of his trunks up to reveal more of his glutes, which is a prohibited move in the NPC (you will be called on it from the head judge). The NPC states your back trunks should be 3/4 over your glutes (although national competitors often don't follow this), & says the trunks must be "decent" but doesn't define what that means. I recall that Lou Ferrigno came onstage at the Masters Olympia in old style trunks, & got made fun of by other competitors.