I don't think there's anything wrong with being a diehard fan/fanatic of a brand (Sony, Microsoft, Nintendo, Apple, Android, etc.) it's when you cross that thin line over into fanboyism. There's like three skips over into that territory: failing to see faults, defending those faults when alternatives offer...better alternatives, and joining in heated debates that spill into the mayhem KMJ_84 mentioned.
From the PS3, Wii, 360 period:
"You $onyians have sh**ty PSN with your downtime and sh**ty security and sh**ty mcsh**cakes. Your mother's a wh***."
(When you pick your console, you get use to downtime if there is downtime and you develop a degree of trust in the security. Plus...paying to use your internet just doesn't seem right however you frame it. Especially when your two competitors are offering it for free...and my mother's a saint, you bastard.)
"Have fun playing your kids games, multiple Marios and Zeldas, and no third party support. Nintentards."
(...and yet you're dying for Nintendo to collapse into 3rd party territory so you can get Nintendo games on your consoles and raged hard when Bayonetta 2 was announced as Wii U only? Plus you're the last person who should say anything about multiple Marios and Zeldas if you've played any title where the gameplay has changed very little across sequels.)
*after getting news that an AAA title would not be coming to Wii* "Well f*** then, that game is [overrated/boring/sucks]. So whatever."
(C'mon guys. I LOVE Nintendo, but c'mon now. Skyrim overrated? GTA series overrated? *sighs* Just because it's not coming doesn't automatically just make it overrated. Chill with that, man.)