The worst for me isn't necessarily the filthiest.
The worst came from an Aussie overseas. He had averaged 70 all season and we were playing them in the last league game - a few county coaches came to have a look at him as he mooted ideas about staying as a kolpak player.
He didn't kick the day off well - we were really short so we had to call up an opening bowler from our thirds - who then went and castled him second ball, for a duck, with a full toss hitting half way up middle and leg.
He then came on to bowl later in the game and fair play to the guy, was pushing 75-80mph, but doing nothing with it. So much so my mate and I were clearing our front legs and just smashing him down the ground or over point.
This is where the worst sledge ever came down...
"Stop backing away you lady garden. If we were in Australia right now, I'd kill you with a bouncer"
This stunned not only me but his own team (They began apologising for his attitude and saying he had got all big-time since his success).
Funnily, before they began apologising, the batsman at the other end, generally one of those rare quiet/nice people - took his lid off and went "But we aren't in Australia are we. So back to your mark, Skippy".
He was so angry, the next two balls were 'bouncers' (Dusty, but slow track) and was taken off by their skipper.
Purely the worst because it was the most pathetic I have ever seen.