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1.
Copping a feel on a girl without ever making out. Most commonly occurs at parties or dance clubs. Named for the circumstance in baseball when a player hits a ball and it bounces over the wall. He automatically advances to second base.
Person 1: Dude, did you see me grabbing that girl's tit when we were dancing? I totally just got to second base in like 5 minutes.

Person 2: I'm not sure if that qualifies as second base. It's more like a ground rule double.
by gabulldogs123 July 28, 2008
 
2.
Having cyber-sex with your significant other. This is referred to as a ground rule double because even though you may think you are going pretty far, you can ultimately only get to second base.
Eric: "How did your Skype conversation with your girlfriend go the other night?"

Sean: "Ground rule double every time bro!"

Mel: "LOLS"
by BerkeleyStudentFoodCollective September 23, 2011
 
3.
When a chick (accidently) touches you with her boobs.
Guy: That chick just totally ground rule double'd my shoulder for a good 5 seconds.

Dude: Awesome.
by Dref321 October 04, 2009
 
4.
When with a women you start off by swinging for the fences but something happens to where you are forced to stay at 2nd base.
"I was with this hottie last night, but my brother kept walking in the and out of the roomie, so instead of a home-run, I got a Ground Rule Double"
by LSD Loudmouth July 28, 2012
 
5.
When a guy finds himself in an unclear sleeping situation with a woman, he is entitled to "take second base" without comment or condemnation.
Guy #1: "Yo, I heard that (insert female name here) crashed in your bed last night."
Guy #2: "Yeah...nothing happend."
Guy #1: "What? You declined a ground-rule double!"
Guy #2: "Shit! Did I really?"
Guy #1: "Yeah, you were definitely entitled to boobie touch-age."
by Cal Ripken Jr. March 16, 2011
 
6.
The scenario is such that you have a kiss and a promise from your old lady but you are not confident that she will deliver later on. So you have the forethought to masturbate in the morning so if it dosent work out with her later you don't become a testosterone filled mad man. So contrary to a double header which would require one to have sex twice in one day this would be considered a Ground rule double should she conced to sex later on.
Person1: Hey Keith I scored a Ground rule double yesterday.

Person 2: What the hell is that?

Person 1: You know it's when you rub one off in the morning and score with the old lady at bedtime.

Person 2: Oh yeah I did that last Sunday.
by Decals March 03, 2014
 
7.
Similar to an Upper Decker, except you 1st lay a turd on the toilet bow lid. You then remove the lid from the upper tank and rapidly fling the toilet bowl lid into the open position, catapulting the turd into the upper tank. This is worse than an upper decker, because not only does the owner have a turd to fish out of the tank, but they also have a lid that requires cleaning as well.
Q: Why is their poo on the toilet lid?

A: Damn it, someone hit a ground rule double before they left our party!
by MerkXRTurbo April 15, 2011