He usually takes out the infamous tiki mask or another trick to frighten the hell out of Courage to bully and to laugh at him, and Muriel slaps or smacks Eustace with the infamous rolling pin or another object to punish him for scaring Courage.
Courage: AHHHHH! *runs off*
Muriel: Eustace! *smacks Eustace with a rolling pin*
Eustace: OW!! What'd I do?
Courage: (sighs after he stops and talks to the audience) I deal with this every day! But at least Muriel smacks him with something...