When a man is having rapid intercourse with a woman and another man sticks his dick to the first mans dick (side) and the force from the first dick pulls the second dick into the woman along with it.
Harry: Last night I went into Dave's room while he was fucking his girlfriend and I started shirt tailing myself in.
Dave: Yea dude, what was up with that?
Harry: You shouldn't have left an opening.
When wiping and you accidentally use the back of your shirt to wipe your ass, leaving a skid mark or a tail. This is usually done when wearing a dress shirt. It is always unintentional
Although I have never personally done this, I do believe it to be theoretically possible and it has likely happened at some point in human existence.
I need to go home, I justshirt tailed myself in the men's room.