My idea

The lamest superpower is one that cannot be displayed to other people. It is also impractical, useless, possibly gimmicky, and uncool. Maybe you can turn white objects white.

What is a superpower? It's a personal power that only you have. It's something that only you can do, and it's supposed to be powerful and awe-inspiring.

What do superpowers do? They allow you to change things. Off the top of my head, every superpower I can think of changes something in a way that no one else can. Either it changes the power's weilder or the world around the weilder.

I would define superpowers as tools used to change the world. Maybe the tool is blunt, like the ability to shoot fire. It only burns things, and you can only use that ability for certain tasks, but it's a tool nonetheless. So I would say that all superpowers are tools.

So the lamest superpower is something that everyone can do, and it changes nothing.

Maybe you can take a Syndrome approach from The Incredibles. "And if everyone is super, no one will be." But no, I don't think that's an acceptable answer.

Could you just intuitively say that the lamest superpower is something dumb, like being able to fart louder than anyone else? Or make your arm hairs stand up on end at will?

Maybe. But I don't think so. I think it's good to look at it logically and seriously. I like what I said before: "The lamest superpower is something that everyone can do, and it changes nothing." I think it's a good rule of thumb for the "lamest superpower", and by using it, you might come up with a superpower that's unarguably lamer.

I have an idea for the lamest superpower, but it might actually be a little interesting.

So maybe the lamest superpower is one that gives you the physical abilities of the average man. Take me for example. If I had that power, it'd do nothing to me. It wouldn't change me, it wouldn't make me different from anyone else, and it wouldn't give me any advantages over weak people that I don't already have. If you give this power to a stronger man, it'd make him weaker. If you give it to a weaker man, he would certainly have experienced personal growth, but he would still have only risen to yet another level of mediocrity, albeit a higher one.

On second thought, you could say that the lamest superpower is one that makes you weaker than the average man. But I don't think so. It'd be like having an ability that gives you some sort of degenerative disease. It would be terrible, negative, and would simply suck, but I'm not sure if it falls under the category of "lame". If a guy had the ability to generate fire, but the fire burned him, you wouldn't say "lame". You'd say, "poor guy". You'd pity his poor lot in life. If you had the powers of an average man, no one would care about you. Imagine standing in a bar and declaring that you had those powers. What the heck? Who cares? It means nothing. It changes nothing. Having the physical powers of a weak man is pretty bad, but I wouldn't call it lame. But getting a superpower that designates you as average and easily overlooked? I think that's lame.

Hmm.

I think I talked too much and tried to explain too much at the end there.

Maybe instead the lamest superpower is one that you can really make fun of, and if that's the case, there's too many to list.