I once heard, "Kill your enemies with kindness - it will drive them crazy." Stay neutral in your choice of gifts. Whatever you do, respect her as your spouse's parent. If you dis her, you are dissing him as well.
Mags above makes a really good point about retaliation. If you have to get her a gag gift for a family gift exchange, that is one thing, but if you just want to give her a gag gift to mess with her, that is altogether different. Just be careful about what you select. Anything you give can and will be used against you in a court of (mother in) law!
Oh my, you are really trying to stir up the pot. I do not believe the meaning of Christmas is to get someone to dislike you more. Why do that when you can spend your time and energy doing something good. Trust me, I was the least favorite person in the life of mymother-in-law. However, I decided never to give her any valid reason to dislike me. I did just the opposite! I tried to give her gifts she would love! It did help make things a little easier on my spouse, which was worth the effort.