We can't see that the standing man is revealing his cock to the other man, but his robe is plainly open and there's no reason to think that he is not naked under the robe.  He's holding a towel, so he is likely getting ready to shower, and he wants the other man's white soap which is resting on the locker room bench at cock level.  A bar of soap is something you rub and rub and that creates froth.  To want another man's soap is symbolic of wanting another man's cock and cum.  The standing man is the "top" and the sitting man is the "bottom," lifting his leg as he would in preparation for getting fucked.  This ad is the work of a gay artist.