Hi guys, I let my wife drive the car last night and she came back with a black scar running all the way on the side of the car. Apparently she caught another car's mirror and the plastic must have rubbed off onto my car. It's not dented or scratched, will t-cut remove it or is there something better than that?

Try a little bit of brasso and a micro fibre cloth.
It's far less abrasive than t-cut.

If it is indeed just plastic, try a solvent - meths, turps, etc. find one that works

it actually came off with a washing powder and a little rub, but thanks for suggestions. Lucky her lol