Setting bombs for me is hit or miss because I giggle like a child when my opponent gets close to a bomb. My mind goes to looney tunes and I lose my tactical advantage.
The further a game is from Advance Wars 2: Blackhole Rising the worse it is. If I can't use Sonjas CO passive to kill my opponent's queen with no chance of retaliation then the game sucks.
"Hell no" (or "Impossible" or "Nonsense"), when the attempted move is always illegal regardless of the opponent's position. For example, moving a bishop as if it were a knight.