Use a silly codeword or phrase to defuse an argument.

My wife and I made a pact that we will stop arguing and hug each other if one of us says "red banana".

It can't just be used to shut someone up, it's only useful when you're both angry. Typically someone will calm down enough to remember to say the words then the other person will laugh and the argument will stop. Sounds a bit crazy but it works really well. I guess it helps to make you realise that most arguments are over silly things.

Think one up now before your next argument!