Why do people hate this stuff and associate it with pimply dorito-finger gamers?
Because 40 years ago, pimply Dorito-finger (table top) gamers were drinking it. I've played D&D with some of those graybeards - it's not so much a stereotype as
the truth. If you want to see a bunch of 50-something guys hammering various types of Mountain Dew, find the local old TTRPG group. The cause behind this is partly due to the taste being different (it's not a cola, but it's not bland like 7-Up and it has caffeine) - as an American youth in the '80's and '90's, this was a huge selling point.
Also, in the late 20th Century before energy drinks were a thing, if you wanted to get jacked up on caffeine, you could get a bottle of No-Doz caffeine tablets, or drink a bunch of coffee. Neither of those got you the associated sugar rush you could get from the next best options, Jolt Cola (twice the caffeine of most colas, but hard to find) or Mountain Dew (which had about half again as much caffeine as a cola, and was literally available everywhere).
Water is amazing. It's like
the water of life.