"Chavo?" is a funny (distorted) way to say "Chego?" ("What?", "What do you mean?" or "I don't get it"), though it should be said "Shto" a.k.a. "Chto", except the Genitive case, where "Chego" is correct. When we want to sound funny, we make a funny confused face and utter "Chavo?"
We also have the word "Chivo", which is derived from "Chego" either, but it's used in situation when you are outraged by impudent behaviour of others, who inflicted a very unfair situation on you by letting you down. "Chivo" may also be used to literally frighten your opponent.
Another cool word "Cho?" deserves a particular talk about it, but it's another (long) story. "Cho?" literally means "Shto", but derives from "Chego". "Cho" usually means contempt, scorn, disdain, or profound disrespect. Sometimes it means that one is utterly indifferent to everything around.
The word "Chto" and "Chego" have some other slang or semi-slang forms.
...But the real masterpiece is a relatively modern hilarious sentence-idiom: "A ya cho? A ya nicho. Drugiye von cho - ee nicho, a ya chut' cho, ee srazy von cho!" I think the one who created it, should be given a medal, though it's constructed out of everyday phrases,- they are just brought together. It basically means: "Why is it supposed to be my fault? I didn't do anything. The others do weird sh*t and they get away with it. But hardly i have done something innocent, and everybody puts the blame on me!"