The common phrase "
tap that" comes from the definition of a tap. A tap is an object that you switch, or turn on to make liquid come out. This meaning can be applied to women and/or homosexuals. So if someone points to a girl and asks you if you want to "tap that", he/she is really asking you if you want to turn the girl on, or make her horny, and then make her "liquid" come out, or in other words, make her orgasm her
juices out. Another option from there is to drink what comes out of the "tap", but this usually depends on the quality of
the brew; it might just be fun to let
the tap run...
Example:
The emo kid could not "tap that" because no one could stand his
apathetic mood, but more than that, no one wanted to touch the dried blood from
the cuts on random places of his body.