Personally, I absolutely love how they like to beg for more worms then spit them out when I'm not looking to screw with my water quality, making me change the water twice in a week to keep up. That's super fun.
Another favorite part is when they decide that they want to play pinball in their tank and kill all my carefully grown aquatic plants and move around the decor so that I have to move it around so they can actually enter their hides again.
Another is when they decide they're suddenly afraid of worms and run away from the feeding tongs to thrash about.
But what I like most of all is when they swim up and take a big gulp of air with a giant "BLOOP".
The last one I actually do like. Plus they're just interesting in general and they're the reason why I got back into studying biology.
they'll do the randomest, cutest things without warning 
