If it's on Liveleak, it's probably not some horny inflation fetishist with an aquarium bubble pump, it's probably gonna be some dude sticking his ass on an air hose at a gas station or some half-drunk worker at a shop being silly with the air hose reel at the back wall that everyone uses to clean their shoes and/or blow sawdust off themselves.
If you're pumping air up your butt, it's fine so long as you use something with low pressure, and you stop + wait if there's every any pain, and 99% of pains during air inflation up the butt is due to too much shit up there blocking the flow, but even that can be mitigated by simply waiting a bit before continuing. If you feel pain and ignore it to continue the airflow, you deserve to be on Liveleak. Even then you still get a good chunk of time before something goes wrong (unless you're stupid and using a big pump).
Really the biggest concerns anyone should have with inflation up the butt are:
1. Making sure the end of the hose doesn't have anything sharp on it, because cutting up the inside of your ass can be terrible for your health.
2. Using a small, weak pump of some kind that you can easily stop the second you need to.
I guess you could also include "don't be an inflatee if you've had a history of intestinal surgeries/injuries" too.