I had a boy in a Merc do this to me on the M6. I was at 80 and he came screaming up behind flashing his lights the whole way. Pulled in, let him past, then sat up the c***s arse for the next ten miles.
Eventually let me past, so I just pulled straight back into the slow lane and dropped to 70.
He sat behind me until the next junction and left the motorway.
Immature and daft, but his face was hilarious. Fat balding c**t had gone pure beetroot.