Example :
I have a friend named Brian.
Brian has his XBox so far stuck up his own butt that he still thinks that DOA3 is the best and most realistic fighting game ever made.
Recently, he tried Virtua Fighter 4 Evo on my PS2. And couldn't believe how "real" it seemed.
He is also what I call a "Halo-person." This condition of his finds its roots way back with GoldenEye64, which he insisted was the best shooter ever made despite the fact that Turok 2/Rage Wars, Perfect Dark, and Quake had come out for the 64, and there was a whole slew of excellent shotters on the PC (Q, Q2, HL, etc.)
He believes Halo2 to be the BEST GAME EVER.
He tried playing a FPS with some speed once, TimeSplitters 2, and totally hated it.
He abhors Quake 3.
More?
People who play Madden because they think it is the best football game and will not consider trying another.
More?
I know of people who would never play Splinter Cell because they believe the "true definition" of a stealth/espionage game is Metal Gear Solid.
More?
Even though they have never played, seen or heard Gran Turismo 4, some people are 100% sure that it can't have the best physics, the best sound, or the best graphics compared to "that other game" which they have never played, seen, or heard simply because it exists only on the PS2, which they don't own or play.
I love reading all the posts calling somebody a "fanboy" when the poster is simply being a "bizarro fanboy." (think Seinfeld)
"...yeah, well, you're just an anti-fanboy."
"oh, yeah...well, yer just an non-anti-fanboy!!!"