When a man/woman is destined to break up with their partner and so by sleeping with them you simply accelerate the process, thus providing a useful service, you are then an accelerator.
One bloke talking to another in a pub - "My friend Samantha is just waiting to dump her annoying boyfriend so if I sleep with her this weekend then I am just acting as an accelerator"
The accelerator is a sex move in which the man licks his index finger and tickles the womans anus while taking her from behind. The unexpected tingling sensation is a surprising and highly pleasurable experience for both parties.
Nic: Hey man have you tried the accelerator yet?
Andy: Yeah man i did it last night! She won't have it any other way from now on.