The phrase “what’s up?” is so commonplace that people don’t actually understand the context in which it should be used. I have two responses to this question, which vary based on the situation.
Case 1: I approach someone.
“What’s up?” is appropriate here because they are curious as to the situation at hand. There is a circumstance out of the ordinary that needs to be explained. My response is to explain my situation, and is a nice lead-in to the rest of the conversation.
Case 2: Someone approaches me.
“What’s up?” What’s up? What are they even asking? I haven’t prompted them in any way, so I usually take this to mean “How are you?” People seem surprised when I respond with “alright” or “fine” to this question. Hopefully they are shocked that they didn’t know what they meant to ask, and are grateful for my timely interpretation.
Chocolate Frosted Sugar Bombs 