Umm, if you're gonna pretend to be a cop...
... it's probably a good idea not to pull over a real cop.
I've never understood what motivates people to do that, but it seems to happen a few times a year in just about every state. A kid I went to high school with did the exact same thing a few years back.
The kicker is at the end of the story. Not only was the guy using emergency lights without being a cop, he'd had a few drinks before hitting the road. I think it's fair to say that he's not too bright.