I literally cannot think of a worse pet.
Not kidding – of all the fauna on God’s green earth, there is probably no animal less suited to be your pet than the hippo. The only thing I can think of that might be close would be an elephant in musth, a starving jaguar, or a skunk with rabies. And even then, man…take the skunk.
They are literally the most aggressive and deadly animal in all of Africa, and kill more people worldwide than Great White sharks and lions combined. Outside of shit like mosquitoes causing malaria or white-tailed deer causing car crashes, there is no wild animal more likely to straight up murder you. And not even as prey or to protect young – just because your mere existence in its presence pisses it the F off.
As if that wasn’t enough, they would also require more upkeep than basically any animal you could name. They eat about 200 pounds of vegetation a day (and if they can’t get it, they start eating other things, like carrion, each other, you, etc), and by the way they don’t like the vegetation in the water or any old greens; rather they like to browse nocturnally on land. They require large amounts of territory and a complicated social structure. They are prone to illness and disease. They are incredibly destructive to their habitats, basically plowing over everything and leveling acres in a single day. Hell, if you had to do nothing else but clean up their shit, you’d have to hire a full time labourer working 8 hours a day 40 hours a week. They have phenomenally bad and unpredictable tempers. And should one of them invariably go nuts – which they do basically all the time – they are nearly impossible to kill or sedate. But they will happily destroy any animal that comes anywhere near them.
In short, you do not want to fuck with hippos.