The after effects of inserting the penis into the dirty ass of another. When the penis is pulled out the tip of the cock is lightly covered with poo thus giving it the look of having a mud on the helmet.
Man I was hittin her in the ass and when I pulled out I had a mudhelmet.
A homosexual term for when one guy butt fucks another guy. The "mud" is a crude term for shit in the bottom's anus. The "helmet" is to describe the shape of the head of the penis. When the top (helmet) rams his dick into the anus of the bottom, he gets shit (mud) on it. Thus, "mud on the helmet".
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.