I have a friend who had a second job as a barman. He told me that sometimes customer would be annoying and stupid, treating the barmen as stupid or with disdain "Are you kidding me? This can't be JB whiskey" "Your boss is refilling the bottles with cheap whiskey". Or sometimes, just to be annoying, they would tell "change the glass, this is dirty".
My friend told me that one day, one of those customers was complaining about the dirty glass. Another barman got inside the bar, got another empty glass, got his dick out of the pants, put inside the glass, and then served another whiskey in that glass. "That's what I always do tho those #$%*s". As my friend told me, from that day he has always been VERY friendly to bartenders. This is the way my friend told me the story, and I don't have reasons to believe it is false.
So you can be friendly with that cop and still get even.....