I saw that gag done in a gay-ish indy movie from Australia. I'm pretty sure it was "Tanlines". The kid (maybe-gay protagonist) was hired by a creepy old lady to come over weekly, sit under the table and eat out a girl who was one of his classmates (her niece? granddaughter?) while they had formal tea. She was supposed to be learning how to be unflappable.
It was something I saw on netflix. Not great production values, but a fun little movie with some serious bits. I recommend it.
Note: When I searched for that image, I saw what appear to be a number of links where you can download it or stream it.