OK, this is a totally off the wall question. I have been reading about trans-Neptunian objects and the small mini-planets that are found 35-45 au's out in the solar system.

So my question is: what if one of these bodies slammed into Neptune and ignited or caused an explosion of the hydrogen(80%) atmosphere of Neptune. I know it's not very likely, but I'm sure it would be visible from Earth. Would it have an impact on us other than a neat light show?

I don't see how Neptune could just "explode" - sorry. The fact that it contains a lot of hydrogen is not terribly relevant - if you're thinking that it would go "poof" like Alderaan in "Star Wars," remember that (a) you need oxygen to burn hydrogen, (b) there's not much oxygen in the Neptue atmosphere, and (c) even if it could burn, that's all it would do - burn - not explode.

Why did you pick Neptune for this disaster? It would be more interestring to think about what would happen if Jupiter suddenly disappeared. Without Jupiter acting to keep the asteroids and comets under control we on Earth would experience greater danger from extra-terestrial impacts. So there would be a much higher likelihood of an extinction level event occurring, and that would definitely ruin your whole day!

Agree with ebains. Jupiter acts as the mother hen with a dustpan for the inner planets of our solar system.
Considering neptune is already visible from earth, depending on the time of year you would see this hypothetical and implausible explosion. No it would not likely have any direct effect on us. The most likely outcome would be that the remaining debris would stay in it's current orbit around the sun as it has for the last few billion years and that orbit would be considered an asteroid belt.