Speaking of the DCCRPG playtest, I mentioned that I played a wizard. What I didn't mention was that, because the game uses oldest-skool character generation, my wizard had an INT score of 5. So I had the opportunity to be a dumb guy.
The trick is to be memorably stupid without being someone who ruins the fun for everyone else. As always, the most important thing about an RPG is that everyone involved has a good time. So I knew that even though Katada Demonbeard was going to be a man not overburdened with brains, he had to be someone that other people would find entertaining. Stomping loudly into the wrong decisions was just going to be annoying in a one-shot game. Instead, I stomped loudly into the right decisions, but for all the wrong reasons.
Why would we go into the dungeon? Not for the fabled hoard of gems -- what a ridiculous story! But the rumors of an underground lake of molten chocolate, created on the fly and expounded upon with some gusto, kept me going in the same direction as everyone else. Several times, I cast a spell for some ridiculous and ill-conceived reason, but it was (almost) always a spell that helped the party in some way. I had a lot of fun with it, and so did the other folks.
There's a difference between a dumb character and a dumb player. If you're making good decisions as a player, they can be dressed up as bad decisions made by the character.