Amateur guitar players

[Zeddo]

Well some really want to show their skills and think that they are the best. I have met only few people like that

[rjohnstone]

Insecurity does that to people.
I've been playing over 40 years and I still think I suck. :p

[Number Of The Priest]

This behavior is endemic to any hobby, leisure activity, or even field of study where a community (whether online or offline) exists.

[paranoid]

Welcome to the forum. I sure hope you have not come here to be one of those you speak of in you op.

[Edward Dreckpack]

Why are most recreational guitar players such rude, arrogant, immature, obnoxious jerks?

Because so many people play guitar, there is a lot of jealousy, insecurity, competition and hate, especially at the amateur level.
Such people due to their own inferiority complex will use any opportunity to be condescending and mean to anyone who they think is of a lower skill level, to feel better about themselves. You can observe such behavior on any guitar forum.