Scanners, David Cronenberg's 1981 film that defies explanation (you really have to see it, as any synopsis will sound kind of ridiculous; I'll give a really half-baked one shortly, though) is justly famous for not only its mind-bending narrative, but its torrent of effects, including one scene where, well, a guy's head explodes. Check out this video and see how they did it!
In Scanners, the people who lend the film its title possess a telepathic ability which, in the film's universe, manifests as ability to control another's body, as well as hear their thoughts. Or, you know, explode their heads. (NOTE: if you are reading this, you almost certainly know that.) In the most famous scene from the film, an executive (who is a scanner himself) from the evil ConSec has his cranium demolished by a renegade scanner who is totally not down with ConSec and all their nefarious plans to weaponize other scanners. But how did they do it? Well, prepare to find out how Special Effects Supervisor Gary Zeller and Special Makeup Artist Stephan Dupuis made that head (which belongs to Canadian actor Louis Del Grande, for the record) explode!
And, in case you wanted to see the event in its proper dramatic context, here's the original from the 1981 film:
Well, now you know the answer. So go forth and impress your friends with your new-found knowledge, and if they doubt you, then send them here and let them see for themselves!