FUDD is a corruption of the old term Fuddy-Duddy.
Mirriam-Webster:
Fuddy-Duddy: one that is old-fashioned, unimaginative, or conservative.
In the vein of gun-owners, as stated above, it's the guy for whom anything "new" is likely to be looked down upon, unless it's a top-of-the-line skeet/trap shotgun or sporting rifle of some kind. He thinks an AR is a refugee from a beer-can recycling center and protruding magazines equate to an operator who uses "spray & pray" techniques.
I'm something of a "Fudd" in that I can't really get too excited about plastic wondernines (or 40's), pistols with tactical rails or lasers. I prefer blued steel and wood. But I don't begrudge those who enjoy shooting their overpriced accessorized tupperware.
The opposite of a Fudd is a
Tacticool-Warrior - for him anything more than 4 years old is passe, his guns have rails for lights, lasers, scopes, flare launchers and wind & barometer settings. This is the guy who turns a lightweight small-caliber rifle into a weapons system that weighs as much as a 1918A2 BAR with so many protruding objects that he doesn't dare get close to any vegetation.
Further out on the scale is the
Mall-Ninja - Like the
Tacticool-Warrior, new is better. The primary difference here is that the Mall-Ninja originally starts out accessorizing his
AirSoft guns but doesn't limit himself to just gun accessories. BDU's with knee & elbow pads (Freudian, methinks), jump boots, thigh holsters and tactical vests are big topics of discussions. When old enough to purchae firearms they become Ninja-Tacticool-Warriors, dressing up in their BDU's & "combat" gear to impress people -- such as the 19 year old I met at the range one day who told me how tough his MOS was in Desert Storm (when he was about 9 years old). The one basic truth about Mall-Ninjas is that they are truely legends in their own minds.