/b/ is where all the 12-year-olds go to get their fix of DEM MEEMS after they're done with lolcats. It's a bit like Xbox Live, except instead of their seething vitriol having context, they choose instead to emulate everyone else. It's where the noncomformists go to conform.
/r9k/ is like the hipster little brother of /b/ and about a hundred times funnier in that sad, ironic way.