1st base: kissing and maybe some 'under the sweater' action
2nd base: french kissing and fondling
3rd base: naked bodies rubbing together, but NO penetration
4th base or home run: sexual intercourse
It got stupid to say 4th base and saying home run during baseball season could be confusing. So the act bacame The Big Nasty.
Nancy: No Suze, we went all the way. Enjoyed The Big Nasty, donchaknow.
The Big Nasty: "Boy, I would suck a fart out of her ass."