1. E-CLUSI-E NIGHTCLUB
I'm guessing you've seen this already. It's been all over the place. I have to assume that this girl isn't really super stupid. She's probably just nervous about being on the show and then excited about the possibility of getting that $10,000. Still, even if she couldn't get the X or V in exclusive, I'm sure she can certainly protect our American liberties.
2. ALL Y-U CAN EAT TAC- BAR
These people might actually be stupid. It's hard to say. Maybe they just grew up in a place where nobody ever ate tacos. Between the two of them, you'd think they could guess it, though.
3. Can I Have A C?
These people are almost certainly stupid. There is a big board that shows the contestants which letters have already been called so there's really no excuse to make that mistake, especially more than once.
This guy isn't stupid. I don't know if he's smart. But he is a damn good guesser.
5. ---S-- -R----R -S -R. -R----R -R---
And before you judge all contestants based on just these few, take a look at this woman who knows exactly how to use the category and the helpful punctuation clue to figure out the puzzle with almost no letters.