Is it rude to order soda at a bar?

Like I don't understand why bartenders roll their eyes and get so upset when people order like a Coke while sitting at a bar. It's like if they want full service and are by themselves, why can't they order what they want? Some people are tired of dealing with overpriced drinks. They are paying for it and tipping either way so why be an about it? And if you are an ***, you won't get tipped anyway. So please explain why it's rude to do this?