Go on and put one hand behind your head as you stand there feeling yourself and imaging yourself being fucked. As you do, begin focusing more on your ass, rubbing your cheeks, your crack and your hole through those flimsy panties. Think about a cock or a dildo being thrust repeatedly in your ass, reaching deeper inside you and stretching open your tight hole.
As you rub your ass more furiously, imagine that cock or dildo being taken out of you ass and thrust into your mouth, forcing you to taste your ass. Imagine that cock or dildo going back and forth from you ass to your mouth, turning you into a real ass-to-mouth slut.
You want it, don't you? If I had someone with a cock or a strapon come in here, you would totally let them have your way with you, wouldn't you. It's your fantasy, isn't it?
It's clear that you are not far away from being someone who fucks their own ass to someone who allows their ass to be fucked by others.