why cant i have the name Thunder Neutron

Because this is not City of Heroes.

wow ty how it take to fink of that

It has to sound like an actual name, like Phillip Bromley, for example.
On the rules page regarding names, there's a random name generator.
You should try that.

yeah Teyacapan Quetzalxochitl
sounds like a real name

not

Perhaps you can't pronounce it so it sounds like an actual name.
It doesn't have to sound American either, and
Because you seem unable to find the random name generator,
click this link:

Random Name Generator

Mocking helping members doesn't really help your case either ...

Handles have to sound like names, not neccessarily human names. Also even if Teyacapan Quetzalxochitl was unacceptable that does not mean further unacceptable names should be accepted, that would be stupid.

"Thunder" and "Neutron" are both actual words. "Teyacapan" and "Quetzalxochitl" are not and are both plausible names (Aztec, even). These rules are clear on the Character Creation rules that your rejection mail links to, so please read them before requesting a handle. Your name will be the name of your character, not a nickname for your account, so select a name accordingly.