Interesting "thanks for being DM" i actually liked...
So recently at SLC (the best hands down employees work at SLC in all of DL) I was checking in and dropping a bag and instead of the usual "thanks for being (blank, insert medallion level)" we all get at check in or when boarding he said "thanks for keeping me employed and my family fed, what do you do that keeps you in the air so much?"
Not a big change necessarily and I am sure the next 7 DMs after me he said the same thing but it was unique and felt like he was genuinely thanking you and instead of reading the DL script came up with a unique way to thank you and engage in conversation at the same time.