A few over the years. I've also had one that was a pan dumper, we have a lot of sand so letting her eat off the ground wasn't a good option, she got a bolted corner pan. You could see her cuss you in her head about it for awhile but she got over it.
Dynasty, not necessarily a eating habit but it involves his feed pan. If he gets anything in his water bucket, a few pieces of hay, his water is lower than his liking, heaven forbid he poops in it, etc he will take his feed pan and put it on top of his water bucket. I am pretty faithful about scrubbing buckets about every 3 days but he lets me know if it needs done. He doesn't put it on there when it's sparkly clean. Spoiled I tell you.
Had a few that like to eat/drink strange things if that counts. My old dun mare I showed as a teen loved oreo cookies & mt. dew, she got both after a good day in the show pen. My sister always swore she rode better on show days because she wanted that treat. Had one that also ate hot dogs. My mom's old mare was a Coke (the soda) addict. She made the front page of the Indy paper one year after she stole the judge's can of coke from her hand in the middle of a showmanship class.
Then I have Woodstock who thinks he wants to eat anything that anyone else is eating. We share a Guinness once a week (I drink my half first of course), he's stolen my lunch a few times, ate ritz cracker & cheese with my kiddo, helped himself to a lollipop once, popsicles, only thing I've found that he didn't like after he stole it was grapefruit. The face he made that day was priceless