How to be Insulting at Christmas: Buy crackers without any little gifts inside. If you have the time beforehand, put unpleasant little remarks and observations inside them instead. You might try to glue the paper hats together so that they tear when the guests try to open them.
How to be Insulting on the Beach: If there's enough sand, dig huge walls around your site and try to put your neighbors in the shade.
How to be Insulting in Church: Arrive late for any service and arrive noisily. Forget at least one, if not both books, and try to make others stand up while you go back for the ones you need.
How to be Insulting Abroad: Insist on paying for everything in sterling.
How to be Insulting in Hotels: Call room service last thing at night, when the kitchens have just been locked, and ask for a cheese sandwich and a glass of fresh milk. Make sure that you leave them untouched and conspicuous the next morning.