Stuipid (in terms of intelligence):
Mihoshi from Tenchi
Stupid in another sense:
Kagome (Inuyasha) in a way; she sort of acts like your stereotypical dumb teenager sometimes, IMO. I used to be a InuKag fan, now I'm all for Kikyo x Inuyasha (even though Kikyo was greatly annoying in the past). So....she's even kind of pointless.
Goku (DBZ) with some of those off-the-wall decisions he made....but I guess it at least did some good).
The stupid category is hard for me because most anime characters I've seen have average to very high intelligence.
Now
weird isn't very hard:
Aburame Shino (Naruto)--This guy is just weird. I can't figure him out.....
Rock Lee (Naruto)--He's one of my favorite characters, but I think he's can placed in the weird category.
Android 16 (Dragonball Z)--........
Pointless:
Uub (Dragonball Z/GT)--I could be wrong, but he seems to have absolutely no purpose. Buu should have just been defeated, IMO.
Sesshomaru (Inuyasha)--Ok, so the rivalry between Sesshomaru and Inuyasha can be entertaining, but I cannot think of a real reason why he exists (no offense to Sesshomaru fans

).
Kagura (Inuyasha)--Even though I like her, I still say that she's pointless.