To do that which is both unnecessary and uncalled for, for the purposes of self-amusement. Always has a victim, often oneself.
In order for something to be a genuine Castaldo, the thought process behind it must be made immediately before the act, but in a form of retroactive hypothesis. The idea is that before you perform a Castaldo, you think about how amusing it will be in retrospect, as opposed to how irresponsible and dangerous it is in the immediate future.
Origin; Italian-American - New Jersey.
"Yes, I'm leaving you with my car keys. Don't Castaldo like last time: It took forever to dig that hooker's fingernails out of the grill."