Hate is a strong word...
There's a song lyric that goes, "Hate is a strong word, but I really, really, really, don't like you." I don't particularly love the song, but I do think it's a good hook. That line applies to a small number of customers in the restaurant.
Yes, I know it's a service business. Yes, I know it's my job to cook food for people, and their satisfaction is the reason the restaurant exists. Yes, I know I chose this career and can get other work.
That's not the point. My point is that in the small scope of serving someone a meal or a cup of coffee it's surprisingly easy to have someone get under your skin, and yes, to really, really, really not like them just in the limited timespan of that interaction.
Maybe it's just a bad first impression within that context ... that happens everytime they come in.