The following will make me sound like a douche, but it's true.
I pay for a service, that's what the cost on the menu is. If a menu tells me a pub lunch will cost me £10, that is how much the pub lunch will cost me, and if the only service that I get is an average tasting meal in average surroundings, that is what I pay.
If, however, I am given good service, such as a well cooked/enjoyable meal, a waiter who is polite and smiles, quick service, decent availability during the meal (in that if I need something and signal to a waiter, someone is available within around a minute. I know that busy times happen, and I'm not going to throw my toys out of the pram if the staff are madly taking orders rather than dropping everything to come and see me, but I also don't expect to be completely ignored) and generally making my experience a good one, I will tip the 10%, possibly up to 15% if the service has been exceptional. As it's usually one waiter who goes above and beyond, and I know tips usually get split at the end of a night, I try to make sure that 5 of the 15% goes directly to the MVP, so to speak. Additionally, I always make sure to thank that person, and let them know that I'll be coming back because of their service, and recommending it to others.
On the other hand, if the waiters are rude or deal with me as though I'm just another walking wallet (I know restaurants only need customers for their money, but if you can't be bothered to create the illusion that I'm being sold a luxury service, I won't pay you luxury prices.), if the waiter asks me to repeat my order several times whilst they're taking it, if they're constantly at the table asking if I'm alright (two or three times during a meal, fine. Outside of this, if I need anything, I'll let you know. Nothing spoils the enjoyment of an evening quite as much as being asked if I'm enjoying the evening repeatedly). If the food is bad or cold, or generally if I have an unenjoyable evening and it's as a direct result of the staff, there is no tip left. I leave the establishment, and don't return. If asked about it, I will let people know about my experience, but unless they really *really* fucked up, I still wouldn't go out of my way to recommend against it.
From the original post, it sounds as though the poster works in a fast food place. Regrettably, I don't usually tip before I've eaten. I've paid for the food. The sum total of the service received is "the guy behind the counter has taken my money and I now have food". I don't know if it's good food or bad food, and as I'm unlikely to eat it in the same place I bought it, that eliminates all other reason that I have to tip. Sorry bro, environmental hazards or not, I've paid for a fast-food pizza, I've been given a fast-food pizza. I wasn't given any more, so I won't pay for anything more. If I get takeaway from a new place, I generally don't tip. If it's good, I'll order again and tip depending on how quickly it gets there, plus a couple of other bits. If it's bad, I won't tip, and if it's bad twice in a row, I won't order from there unless there are some mitigating factors.
When I mentioned "a couple of other bits", a sense of humour goes a long way. There's a local pizza place that does deliveries, and every time my mates and I order from them, we ask them to draw something on the box. Nothing massive, just stuff like a wizard, a dinosaur or a chicken. If the drawing's on the box, the driver gets a fiver, a tenner if it's a big order. If it's not, they don't. Simple. A few of the drivers have actually started carrying magic markers in their glove compartments for this exact reason. Life is better with a little humour.
TL;DR - a tip is an extra payment for good service. Give me good service, I'll tip you decently, but don't just expect it for doing the bare minimum.
