I gave big tip when they served me that ipad to pay my very first time. There was no option to waive the tip but if you hit custom, it shows no tip option. If it a service like sit down eatery then yeah, tip but if I'm just buying a soda pop cola from the fridge, do I need to tip? You know people do tip starbucks' barista right?
Kind of a deceptive way to get the gullible and dumb like your boy hmoobrock there to pick a card and any card he picks, even if it is 10% tip, he will still complains about it.
Tip money is nothing as it will not bankrupt you. You shouldn't tip if the service is bad. The most cop out excuse for not tipping is..... well, I don't have loose change. I only have $100. Tell them to break your bills you noob.