I have two. The first is the first 5 minutes of Cobra. TERRIBLE movie, but those 5 minutes are gold. Best part is when he tells the dude to "drop it", waits 2 milliseconds, then pumps several rounds into chest.
Second is Frankenhooker (1990). One of my buddies had this on VHS and the premise is ridiculous. Inventor boyfriend creates a remote controlled lawnmower and accidentally runs over (chops up) his girlfriend. Said boyfriend then figures out how to resurrect her but he needs body parts. Enter Super Crack, another invention of his that causes the inhalee to blow up after smoking. The boyfriend then salvages the parts to to put his GF back together again.
For those interested you can see it in it's entirety on youtube. The highlight starts around the 39 minute mark where Jeffrey (the boyfriend) is inspecting hookers to see if they have the right parts. He decides not to go through with it but the ladies find his stash of super crack, start smoking, then blow up. The editing/cuts that go from the women screaming to still of mannequins being blown to bits is hilarious. Due to some nudity I'm not going to link the scene directly.