Someone who interferes with the signing of an important contract or document.
1. B: Uh, I wouldn't sign over your power of attorney to this guy, he's doing that sinister laugh that people do in movies.
Guy: Hey, buddy, don't be a hancock block... who are you, anyway?? (sinister laugh)
2. He was right about to sign the confession and then his lawyer came in and totally hancock-blocked me.