Definition of "kryptonite"

The terrific seven-grain bread here is the kryptonite of restaurant reviewers: two mini-loaves and you are incapacitated.

1991 October 25, Bryan Miller, “Restaurants: John Clancy's”, in New York Times‎

So while recording or sampling a Charlie Manson track […] makes for shock rock kudos aplenty, a devotion to Hubbard is kryptonite for credibility.

2006 March 25, Jonathan Leggett, “Cult musicians”, in The Guardian

We all have our own kryptonite or kryptonites, so don't tempt yourself by listening to so-called friends who are just demonic tools being used to bring you under.

2016, Marlon Orlando Cole, Orphans: Nature's Beloved, page 93