Gonna pull a list on this one:
Send in an outfit type and I'll show you my muses average outfit for...
It depends on the formal event, but heres a couple of ideas uwu second one drawn by me <3
If we're going for a MODERN concert, he'd go ALL out. This would probably be a rare occasion tho, since theres not much modern music he likes. But if its a celebration of sorts like pride? Hell yeah. If you're thinking concert like a orchestra or something? He'd just wear pompous thingies similar to the formal wear.
Halloween would depend on if its a costume party or not :D I've drawn him in a few costumes
Winter? Still gotta wear that pop of colour and a cool hat