Curate, connect, and discover
Imagine Starscream learning about human behaviour and mostly the internet.
And not on the 'aww he secretly still has a heart of gold' (honestly hate that). I mean in a way he only did it cause he was bored and only had human internet available.
And also for new insults he can use on Megatron without being understood so he can get away with it (he still gets abused cause Meg knew what he said was an insult) and cause when he says Cybertronian insults to humans they don't understand. He's just stepping up his roast battle game.
And soon others join in because they can't let Starscream have all the fun. And then Autobots (I know they hang out with humans but I think that they didn't dig into the 'mean' stuff) join in cause the battlefield was starting to be dominated by the decepticons due to the enormous metal damage.
And that's how all Cybertronians started to use human insults. Yeah I headcanon this now