Where I am based, one renter started up with the towbar attached. He took ~ 1" x 1" piece out of the prop, chucked the mangled towbar into some grass, went for a flight, landed, said nothing. I saw the dent myself. The school never got anything from him, so it was an insurance job.
Sounds completely reasonable. I mean, if you hit a stone with a lawn mower, and it runs OK afterwards, you just carry on, so why should a plane be any different? The engine looks and sounds pretty similar to a lawn mower, and is even harder to start.
I am saying this only ~50% tongue in cheek, because PPL training does not mention shock loading at all (IME) so if the "pilot" is merely trying to avoid getting into trouble, it's perhaps not all that suprising. One should judge people only by reference to their training.