It depends on which way you are amending the suggestions as to whether or not we can call you an asshole. Suppose the on-screen suggestions are amounts such as 18, 20, and 22 percent, or their dollar equivalents, and you are choosing to tip higher than these suggestions. In that case, you’re not an asshole, but are instead, someone who values the hospitality industry and good service. You also might be a regular who doesn’t mind a free perk every once in a while from a staff that notices that you value them.
If you are amending the suggested amounts to tip lower, or not tip at all, you’re at best a cheapskate, and at worst, an asshole. If this is you, don’t be surprised if the service you receive isn’t the most pleasant, especially if this is a spot you frequent regularly. Regardless of your opinion on tipping, this is the system we have in America, and it’s responsible for the majority of a service professional’s wages. That’s just the reality. Choose to do with that information what you will.