DOOM did give me the occasional brown-trouser moment (though not as badly as Dungeon Master on the Atari ST) but it also gave me one of my most enduring laughs that still makes me snicker today when I think about it.
Multiplayer via modem in about 96ish, me and a mate are death-matching one night on some new PD levels we'd got hold of. We were pretty evenly matched and knew the stock maps backwards, so the only way we could really get the drop on each other was to use downloaded DEU-created maps we hadn't played enough to learn by heart. I find this room with a high ceiling and a central pillar that recesses up into it, and a switch. Hit the switch, down comes the pillar, and there's an armour power-up tucked on top. Nice.
Hmm. Does that pillar go up again? Click. Ah, yes, it does. Click. Down it comes, click, run-jump, and now I'm on the pillar heading upwards. Oh, I wonder if there's space in the ceiling cavity for me... yes there is. I sit tight, and wait.
About 10 minutes later, my mate finds the same room. Sees the pillar, and the switch. Click.
Down I come, stock-still, looking just like a static Marine model. I look at my mate all the way down, and he looks at me, wondering why there's a Marine model hidden on this pillar.
Then I BFG the smegger. His only response: "You slag". I laughed myself sick.
It's making me giggle even now.