Well, since almost all Characiforms are carnivorous or at least omnivorous, almost all of them have teeth of some sort. There are a few exceptions, especailly as the families and species are continuously juggled as new grouping keep coming up, but almost all of them have teeth. Which, simply means that they almost all will nip to a certain degree. But lemons are generally not that nippy. Yes, there are always individuals whose personalities will not follow generalities. Especially compared with several other of the tetra family, like serpae tetras as much, much more notorious nippers. One thing that will help dissuade any nipping is if the lemons (and this goes for many other tetras, too) are not top dogs in the species. A completely peaceful, yet larger, other fish in the aquarium will let the lemons know that they are not in charge. When they are not in charge, they usually will not bully other fish at all.
I hope the OP does choose lemon tetras, though, they are one of my favorite fish. They usually are stressed in the dealer's tanks, and almost always look so washed out and plain, but if you get a school home, given them some high quality food, and water, and some good plants for cover, they will turn the most brilliant yellows. Live food will especially help, but mostly TLC and time will make these fish as brilliant and colorful as almost any other tetra.
