He agreed to wear it after having dinner with the Low Talker.
Just like Jerry and the Puffy Shirt.
Kramer: Youuuu... could be a uterus
Kuz: But I don't wanna be a uterus! Then I'll have to do uterus things! I'll have to ovulate ! And bleed once a month! I'll have to house fertilization! I'll have to house eggs! I'll have to hold a fetus so it doesn't strangle itself! No Kramer! No sweater! No uterus!
Kramer: Kooz, do you not recall eight summers ago, when I ate that rotten papaya that you left out for that Japanese med student you were dating... Thus avoiding a rather messy night for you in your bed with... Madame... Butterfly? I thought we were bros, Kuz... Bros!
Kuz: (through clenched teeth) ALLRIGGHHHHTTT!