I’ve seen this everywhere but I thought about it again today as I watched the South Park movie. After Kyles Moms A Bitch, Kyles mom is, obviously, standing right behind Cartman.
Is there a documented first use of this trope? It seems like its a meta play on something original but this it’s seems like it’s been around since the beginning of time.
I’m pretty sure I’ve seen it in silent films, so I’m guessing it goes back at the very latest to Vaudeville. It may be as old as dirt. Have you tried TV tropes?
TV Tropes’ Right Behind Me page has examples going back to the Victorian novel North and South, but their earliest example of the line “he’s standing right behind me, isn’t he?” seems to be City Slickers.