Use of honorifics - "Chan"

ちゃん is a Japanese honorific, and used like "kun" as a term of endearment, but there are differences between the two. "Chan" does not have a direct meaning in English, but its like calling someone "little" in an affectionate way. 

Use in Noah
"Chan" amongst wrestlers is not usually used, because they tend to use the suffix "kun", which is more masculine. "Chan" is normally used by and for women, although there are exceptions;

1. Takashi Sugiura has called KENTA "Ken-chan", which I think probably goes back to the fact that he's known him since he was a teenager of about 18 or 19 (not to mention that Sugiura is 49, and KENTA 38).
2. Marufuji has used it for Takashi Sugiura when asking Kenoh why he chose to sit between himself and "Sugi-chan". This is an example of using it in "baby talk", which was how Marufuji was basically speaking to Kenoh (i.e like a small child).
3. Kenta Kobashi also used to call (or still does call for all I know) KENTA "Ken-chan", ("Little KENTA"), because the similarity of their surnames "Kobashi" and "Kobayashi" caused instant confusion in the All Japan\Noah dojos, and therefore differentiating between "Kobashi-san" and "Kobayashi-san" was a lot easier when "Chan" was added. 
4. Satoko (Mohammed Yone's female alter-ego) refers to Naomichi Marufuji as "Michi-chan", this is an example of feminine speech. 
5. YO-HEY calls himself "YO-HEY chan" at times, which is an example of playful speech.  

Fans (usually female) also use the honorific as nicknames, the most popular being "Katchan" (Katsuhiko Nakajima), which comes from the fact that he has grown up in Puro. 

"Chan" and "Kun" are not honorifics that would ever be used for anyone like Kenta Kobashi, Yoshinari Ogawa or Mitsuharu Misawa. You would never address anyone senior to you as "Chan" or "Kun", unless of course you had an extremely playful and informal relationship with that person...or else like Kenoh, wished to be very rude, but he uses "kun" in these situations, as its mainly male speech, and he doesn't wish to be playful, babyish or whimsical, but rude.