Due to the common meaning of the last hole on a full golf course, this is the true and sexual meaning of, the '18th hole'.
A woman shall expose her arse and bend over till she is able to touch her feet with her fingers. The male then proceeds to collect a golf ball and either can, kick it, or use a golf club and will attempt to make the golf ball stay or go in completely to the anus or vagina. If successful the male may then carry on with the sexual move he wishes. The '18th hole' usually determines any disagreement in the bedroom. If the male succeeds he can go ahead with what he wanted. If he fails, the woman has a right to still saying 'no'.
Keith: Heather, let me perform a Lancashire Shitter!
Heather: Absolutely not Keith.
Keith: It looks like it's going down to the 18th hole!
(proceeds with 18th hole)