You can’t receive a red card for dissent.
Dissent is a yellow card offence.
Using offensive, insulting or abusive language and/or action(s) is a red card offence.
Straight red for “using offensive, insulting or abusive language and/or action(s).”
You can’t appeal it because what he said was the above!
Really stupid by Dunk and got what he deserved. You can’t go round saying that directly to the referee. Most fans would like to see what happens in Rugby...