Obese people.
I spent the whole day with my girlfriend's highschool friend and her husband, both of whom I'd never met but turned out to be obese (5 foot 8ish and around 300 pounds each).
First of all, oh god, the smell. The husband had this subtle-but-awful constant smell around him, not super powerful, but if you were within 2 or 3 feet you'd get whiffs of it. Definitely BO smell. We rode an hour each way in their car, so I got to experience this smell going up and back. At first I assumed it was the car, but I also smelled it when we were walking around.
Secondly, their fatness pretty much ruined the activities of the trip. We went to Hershey Gardens (big botanical garden in Hershey PA, near the amusement park), and they were huffing and puffing mere minutes in. They had to sit down and rest no less than 3 times during our 1 hour there. For comparison, last year my girlfriend and I walked around the gardens for more than 2 hours without a single rest. This time we both would have liked to spend a bit more time exploring again, but these two heffers were practically dying after an hour in the heat (and I couldn't really stand the smell anymore), so we left. Later on we played mini golf, and they took FOREVER. They slowly waddled from one hole to the next, and just getting from the initial putting area to the whole would take them 20 - 30 seconds on some holes. They also couldn't just bend down and pick up their ball from the hole, because their enormous bellies got in the way. Instead, they had to kind of spread their legs into a sort of sumo squat to allow room for their bellies to swing between their legs so they could get low enough to pick up the balls.
Thirdly, their appearance was just off-putting. They're both the same age as my girlfriend (26), but I'd have pegged them as mid 40s easily. The woman had one of those super round, jiggly double/triple chins like Honey Boo Boo's mom has. All around the base of it, where it rubs against her upper neck fat, it had these blister-looking irritations. I also spotted some hair peaking up from under the neckline of her shirt on the back of her neck. Thank god that was after we had already eaten.
The sad thing is that they are both extremely nice, friendly people. If they were able to perform normal physical activities and they didn't have the gross appearance/smell of obese people, they'd be really fun to hang out with. Fuck people who ruin their health, their future, and their ability to enjoy regular, daily activities.