a male with an over protective mother
that keeps him locked in a "bubble"

A swimmer

Someone who's always sick

boy in the plastic bubble is used to describe a person who must live in a microbiologically sterile environment for medical reasons

A cowardly paladin in World of Warcraft. The name refers to the paladin's spell Divine Protection, which shields the paladin from damage for a few moments, during which time the paladin uses a hearthstone to escape from battle.

Someone who finishes just below being in the money in a poker tournament aka "the bubble".

A horrible movie starring Jake Gyllenhaal. While this movie has no plot at all throughout most of it, girls can't seem to stop watching it.