@PJW: That's not what it means here in California, USA Trippin' is a slang term that means mistaken/saying the wrong stuff/confused/bewildered/freaking out "Don't be trippin" - Don't be confused "Stop trippin out" - Stop freaking out/being nervous "Why you trippin?" - Why are you all nervous? "That girl be trippin out, man" - She's crazy and nonsense, man. :)

everything already said is correct but it seems most often its used in reaction to someone elses behavior. "why you trippin'?" as -"what's your problem?" "he was tripping on acid"/"he had a bad acid trip"-drugs if a boy is hesitant to do something with his friends or is acting unreasonably, one of them may ask: "why are you trippin?"-as in "why are you acting like this?" or "why are you worried?" i heard a someone say "my boyfriend must be trippin if he thinks im going to bail him out of jail again"-as in "he must be seriously deluded in his reasoning if..etc" i also heard a young couple arguing over what street to turn on,the man kept insisting it was a right turn and the woman said it was left. the man realized she was right and said "im trippin...it IS a left on this street" so it can be used as a correction. it can mean "jusk kidding" but its not common here, it does depend where you are. its not something everyone says and definitely isnt appropriate "comfortable language" for professional situations. ive never heard adults say that.

I am tripping = I am under the influence of hallucinogenic drugs.

I'm trippin' means that you did or said something you would not usually do or say, If I was drunk and my friend and I began to argue and I say something mean, or something i wouldn't usually say. While apologizing I could say, " I'm sorry. Last night I was trippin."

It's kind of like saying "I'm kidding" or "I'm joking".