It's me when I can exploit it, and then not me when I can help the party.
I remind the DM of certain minuses the foes get, but tend to "just forget" when it's our turn.
The DM doesn't care really, because in the end, it is a story telling adventure and we can't continue that story if we all die during a kobold ambush.
Now against the main boss he remembers these things, when its 1 monster or so, but remembering all the flanking rules when fighting a horde of goblins?
I don't think even Hitler would bother.