I would assume as a straight guy if you like asses and you are responding to a post in which she mentions not wanting to show cleavage, that by mention that you like ass, you would like to see her ass. Of course there is nothing wrong with that. If you want to see her ass and she is willing to show her ass, then by all means check out her ass. As long as you are both consenting adults and there is no money being exchanged, then more power to you. I mean, free ass is free ass. Don't let me stand in the way.