Tip #1: Never try to carjack anyone.
Tip #2. Never, every try to carjack a cop. It's one of those things that is pretty much guaranteed to end badly for you.
Three idiots found out how bad of an idea it is to carjack an off-duty copy. It happened in the vicinity of the Southfield Freeway and Fenkell, which is approximately 3 miles north of the Warrendale neighborhood. The full story is available here.