There is someone I'm around all the time that has to one up everyone they talk to. It doesn't matter what is going on their situation is far better, far worse, more abundant, or more lacking. If I have one they have two or three. If I have two they've never even heard of what I'm talking about. I can't control whether or not I see this person, what can I do?
These situations call for a lot of imagination. Get good at making up the most ridiculous fantastic situations and goad them into showing their need to compete. By exposing their compulsive competitiveness everyone else will understand what you're doing and join in, or at least commiserate your dislike for the behavior. Hopefully they figure out what you're doing and stop it, otherwise just not talking to them is your only option.
I just started a new job. Within the training class we have a diverse group, including a little person. I realized I don't know if that's even the appropriate term. What etiquette advice can you give me?
You are sweet to think of their feelings, but there is nothing to worry about. Obviously they're a comical bunch, so they must have a sense of humor about it. Finding a cute nickname like Sneezy or Happy will help break the ice. Crouch next to them like you would a child so you can make eye contact. Pat them on the head to reassure them, you've got their back. Above all, never make special concessions for them, they want to be treated like everyone else. When all else fails make light of the situation to break the tension. Hope that gives you some guide posts.