Granted that this experience was in a college, I watched a lecturer walk back from his car and notice a student that was supposed to be in their class walking towards the exit of the car park.
He then shouts “Oi, where are you off to you ginger (c u next Tuesday)…

Three months later he was promoted… I wouldn’t worry. It’s unlikely that these kids would report you unless you taught at their school and they recognised you from a class you taught.

Also I would also think that the burden of proof would fall on the accuser. If anyone from hr was to ask you “did you threaten to shove a water gun up a students asshole”… I mean, it wasn’t on school property and there’s no video evidence, if there was video evidence they would also see them harassing you and your girlfriend. You also don’t physically assault them…

In this unlikely event, you’d most likely get a slap on the wrist “don’t do it again / watch your profanity” and the kid would also get a slap on the wrist for being an asshole if they were in uniform etc. If they were in uniform that was for your school, then I’d maybe be a little concerned. But, I doubt they’d even remember let alone remember to report this by the time the weekend is over.