Firstly, you are a person. The NFT is an NFT - essentially a copyright claim on an image of you. You have not been "turned into" an NFT - a picture of you has.

Secondly, they reason NFTs are stupid is that they don't actually help with copyright - you still have to prove ownership of the asset and enforce it. Rather than "try to stop it", lean in to the joke and use this as a springboard for discussion. This actually proves that point - in order to claim ownership of your likeness, you'd have to take them to court with traditional copyright law. They're essentially just giving away a photo of you. Which is weird and only has the merit of "being an NFT".

Thirdly, if this is at work, this is a HR issue. If you feel you're being harassed, treat it as such. Or, alternatively, personally reframe it - it's not harassment if you get in on the joke.