Doing things badly

[ODFOx]

We're all locked down and I'm trying to work from home amid the bonkers so I accept that I may be overreacting, but my 20 year old has just started cleaning out the microwave. 'Heat a mug of water and vinegar in there to soften the bits before you wipe down' I say, attempting to help. Half a mug of aged balsamic vinegar has just been poured into the microwave and superheated. My child(adult) is not an idiot. Why would he do such a thing except in pretence of incompetence so I never ask again?
It smells like the Branstons factory and looks like a sheet of bonfire toffee. I don't think it will ever come off!

Are you absolutely sure he's not an idiot?

As an outside observer, it does seem like he might be.

Could it have been a case of not listening properly?

Its just another of those ' Mum, how do I...' or ' where's the....' other that have been going on since I've been working from home, he's relatively capable normally.
Tbf, the whole family is at it. I'm going slightly mad....