I used to have this problem. I would think to myself, "man. . .what the heck. . ." then I looked at the DF settings and noticed the "E" was checked/highlighted. I unchecked it, never ran into bad players ever again. Though, I still get a little sad when I see another underlined "E" in the party group when I should be the only one but usually they turn out to be ok.

I'm also on a Japanese server so my exposure to stupid is farily limited if not none existent.