In essence, a nicer term for someone who is a hypocrite, or is being hypocritical. Comes from 'double standards'.
I prefer the term "double standardised".
the act of unfaithfully claiming another person while continuing to label them as a slag in response to the feeling of repeated rejection of the highest level
Soup (Tomato): Hey carrot… You’re looking real tasty today… let me have a nibble
Carrot: No - you’re literally tomato soup. Eugh.
Soup: You little slag
This is double-standardised claiming.