Sensei Trevor's karate class, where I've taken to spending my Thursday evenings, has a simple rule:
"There is no need to apologise in this dojo! You are aware that you have made a mistake, and I am aware also! Innit!"
When someone lapses we all have to do press-ups, one for each word of the sentence above, which we shout out as we go along.
If this doesn't cure me nothing will.