Used to denote something that is so good that it hurts a little (or even a lot).
This would likely be used rarely in the positive, something that is so good that having experienced it, you can now die knowing that you have had the best and are happy.
Most common usage IS in the negative, as is described in the example below.
Everyone tells you how AWESOME something is, like a pastry or a movie. Then you go to that movie and don't like it (or just think it's so-so, or nothing special). Or, in our other example, you try the pastry and it's not "to die for". In both situations, when asked if you liked it, you say "It didn't burn my balls"
Word used to describe something that is your least favorite. Primarily to describe things and preferences, but can also be used to refer to people.
To say most favorite or absolute favorite, people often say "fave". Similarly, for one's best friend they might say "bestee".
"There is nothing good about alfalfa sprouts. They get stuck in my teeth and make all my food taste like dirt. Definitely my leastee veggie."