I'm thinking of getting my husband's cousin a Christmas gift that will definitely make him angry
What kind of item do you think would make him angry?
I'm going to buy him a platinum statue of a dog on a tree.
Lighthearted pranks and harmless jokes can sometimes be funny, but your husband's cousin maybe expecting a gift that is more appropriate during Christmas. I don't think it's appropriate for you to play a prank during Christmas time, so you should probably save this for a less important event.
Nah, I'm going to play a prank on him.
I really don't understand what your motivation is here, but it sounds like you really want to make your husband's cousin angry, and the holidays are not the time for that. This could cause a lot of awkwardness and hurt feelings during a family get-together. If you are determined to play this kind of a prank, either do it in private, or do it after Christmas.