help me with a douchebag from work:(

So I work at this cat shelter, I absolutely love working there and all of the others there are super nice! Now enter this geezer. this mf claims to have a CAT ALLERGY!?!??!?!? WHY ARE YOU WORKING AT A CAT SHELTER IF YOU SUPPOSEDLY HAVE A CAT ALLERGY  IT DOESN´T MAKE ANY SENSE. Aside from that, he's quite unfriendly to the cats and doesn't have any Patience with the cats that have trauma. On top of that he thinks he knows everything better then me just because he's as old as time. I've reported him to my boss and he has gotten a write up, but he still has an attitude when speaking to me and I can't get him to actually care for the cats, I'm losing hope and need ideas that preferably won't get me fired ≽^•⩊•^≼