An angry busdriver is when you're doing your girl doggy-style, and keep tugging on her ponytail - so she looks like the angry busdriver that keeps looking up in his mirror.
Bus Driver's Bum
Have you ever seen a bus driver with a small arse - no, because they are always sat on it!
So this applies to someones whose arse is that bloody big, that it can easily effect tides and cause a solar eclipse.