"vanilla", when it is does not involve dairy or cake, tends to be a synonym for "plain" and "boring", and generally references a proper noun. for example; "mary drives a honda civic, lives in a cookie cutter apartment complex by the mall, and wears white hanes, she is soooooo vanilla" (note, the other bakery reference for "boring" and "generic").
apparently, the non-vanilla "moose tracker sherbert ripplers" are out there piercing their fleshy bits (belly buttons being a popular destination for the gun), inking up their skin (barbed wire/butterfly/dolphin tattoo anyone?), and dying/chopping/shaving/mohawking their hair. they can also be found engaging in acrobatic, yogatastic sex in aeroplane/burger king/your next door neighbour's waterbed, who you are housesitting for while they are away in florida's, bathroom.
"vanilla", as i understand it (and have on occasion been labeled), implies a paucity of adventure, risk and change. oddly enough, the true dictionary definition describes vanilla as a flavouring "agent".