Even though llegar has no special connotation in slang, two of its deratives are highly handy: llegue (JEH-geh) and llégale (JEH-gah-leh).
A llegue can be a little taste of something: le di un llegue a los chiles rellenos (I had a bite of chiles rellenos) or le dimos un llegue a tu huizcacho (we drank a bit of your scotch). It can also mean a minor car crash or the dent resulting from it: me dieron un llegue en la puerta del copiloto (I got hit by a car on the passengers' door).
When used by secundaria (junior high) students, llegarle to someone means to ask that person to be one's sweetheart: mi primo acaba de llegarle a tu carnala (my cousin just asked your sister to be his sweetheart).
In a more general setting, llegarle means "to the get out of here": ya son las 3AM, yo creo que ya le llego (it's 3AM already, I think I'd better get out of here) or llégale a verga (get the hell out of here).