1st base and 2nd base and 3rd base in dating
There are, as the top comment on this question notes, four bases in baseball, and these have corresponding sex acts associated with them.
"I got to second base with that girl yesterday." "I didn't think I had a chance, but I made it to third base with her last night." One of the other answers has provided a nice link to the Wikipedia entry for baseball metaphors for sex.
Speaking of sexual activity in terms of bases, sometimes doing so can make the interaction with your partner(s) seem more goal-oriented (i.e., to “hit that home run”, or “get to home base”).
Keep in mind that sexual activity doesn’t just have to be about how far you can get with someone.
Another crucial piece to rounding any of the bases is making sure that you and your partner(s) have mutually consented.
If we say home base = fourth base, that's 4 4 − 3 = 5, the subtraction because he was receiving instead of giving.
But this is a joke, and probably not intended to be analyzed too closely. Although this wasn't what "House" referred to, Urban Dictionary lists fifth base as anal sex.
First base is equivilent to french kissing, not just kissing. Haven't you two only been dating for a few days?
Second base is touching of private extremities and/or apendages of the partners' body, aka boob touch. Lastly a home run or four bases is full on, big time sex. Person B: Yeah, I'm going to try and see a movie at her house while her parents are out next week, mabye we can get to second!