1st Base - Kissing, open mouth. Also any above the belt touching is included in this base.
2nd Base - Hands below the belt.
3rd Base - When mouths are used below the belt. This base also includes the sex toys.
Home
Plate, (Home Run) - Intercourse
5th base or 'The Dugout' - Anal
Sex.
A
grand slam, would be achieving all of these on a first date.
First, Second, and Third are the typical sexual
bases.
Anything beyond those and you probably aren't using
baseball metaphors any longer anyways!
(Unless of course referring to 'The Dugout', because that's just hilarious!)