Spiteful 40th anniversary gift?

well recently I found out that my firstborn son(40 years old) and the foundation for which my marriage was built on was named after my wife's high school ex-boyfriend, He wont allow me to have a blood test done to see if he is really my son, he said he would rather go on not knowing, so I decided that since she took my 40 year old son I will take her 40th anniversary away, I figure that I will just get her a really lame sweater(with a giraffe on it or something) or maybe a gift certificate for like 25 dollars and I wont even put her name on it. Or maybe I will just buy her a bunch of cheap china from the dollar store or something, I don't know, I just need some ideas, something that will make her think that I have a surprise gift but in actuality I wont!!!!! If she makes me question my marriage and the birth of my son I will make her question her marriage and her 40 years with me, its only fair