Protip: use two fingers in your partner’s bottom so you have him more opened up. Then stroke his prostate with your fingertip, softly at first (almost a tickle), increasing pressure as you go. The additional finger will help give you freedom to move, which he will appreciate — sometimes going in and out causes a bottom to think he might have to use the bathroom, while stroking without moving in and out stimulates the target area better.
The gif slowed down when I hit “reblog” and I saw his balls actually go up above his penis. Now THAT is a good kick.