These are usually young adults who live in their mothers basement who could never be able to hurt you in real life, so they get out all their sexual/social/financial frustrations on the Interweb. Those with keyboard muscles usually have no job/hobby/significant other/family, therefore have all the time in the world to pick pointless fights with intelligent contributors to society.
They usually cannot spell to save their lives, and will try to insult you with everything they can think of. (which usually isn't anything that makes sense, AT ALL.)
The best way to deal with those morons with Keyboard muscles? Kill'em with kindness. It may sound sooo cliche, Just try it! It works everytime. You want to actually get to them? be the nicest you can be. ;) I'm pretty sure it overloads them blows their empty little heads up.
- We also see these types of muscles show on other things, like XboxLIVE- although known by other names. Please see: Xbox Live Dick
Me: Wow, calm down honey. You are so right... I am such a noob. Can I feel your Keyboard Muscles? :)
HaX0r.N3wB.pwner: wtf r u tlkin about it doezt make sentss!!! I hatee u!!!!1