I will never, ever make the statement, "My character is not smart enough 
to think of that."  That would be an insult to the DM who created the 
puzzle.  If I were going to make statements like that, I might as well 
just ask the DM each round, "what does my character think it would be a 
good idea to do now?"  It's the same sort of thing.

Also, I will never, ever create a D&D character whose purpose is to annoy
the other players.  For example, I refuse to create a thief who steals
from the party.  I refuse to create an assassin who threatens to kill
characters in their sleep if they don't obey him.  I refuse to create an
asshole who constantly makes fun of the other party members (but still
stays in the party for some reason).  And I refuse to create a parasite
who can't contribute to combat but still demands a share of the treasure.

I have played with characters who have done all of this.  I did not enjoy 
it.