Yeah, flaming dr. pepper is a shot of amaretto laced with 151. The 151 is then ignited with a lighter, and the shot is dropped into a half-glass of beer. This puts out the flame, at which point you chug away. And chug quickly, because the stuff tastes absolutely HORRIBLE if you let it sit at all after mixing.
151 is the alcohol most commonly used for flaming drinks in bars. Everclear is also flammable straight out of the bottle, but I'd imagine it might almost be TOO much so...and besides that, 190+ proof liquor is illegal in at least a few states.
But yeah, never attempt to drink anything when it's actually on fire. And never tell the former hooters waitress/bartender who just poured your friend a triple shot of 151 in a plastic cup to light it up, because she'll do it, thereby melting a good portion of said cup. That was a bad night.