I remember two I had back in the day, before my driver crashed.
One was... I think he was latino? He mooned his grandma while she was speaking to the camera, and then asked her to turn around so she could see it and burst out laughing.
The other is far less clear in my head, but the guy was wearing orange or red, and we saw his side ass first as he brought his ass closer to his friend's face to shove it into it, I believe. The friend was on the computer, concentrated. Though the details are really nebulous and I may be remembering a lot of this wrong.
I've tried to find them back, but I can only find girl mooning vids from vine so far, which is not in my bracket of interest, sadly.