Justin Bieber taught his beloved, if not brilliant, Beliebers the meaning of the word "refrain." And not the kind you find in a song, either.

Unfortunately, his fans weren't such quick studies.

Bieber was performing onstage earlier this week when his more rabid fans began throwing stuff onto the stage where he was hard at work dancing, singing and working up his sweat and projectile saliva.

To put an end to the hocking, Bieber urged the crowd to "refrain" from throwing things onstage.

Problem is, it looks like his fans mistook "refrain" the verb for "refrain" the noun and just kept on throwing stuff, and when Bieber -- like a slightly irritated, mildly condescending but sweet kindergarten teacher -- explained the definition of the term, they responded by, well, not following his instructions.

Instead of throwing presents and candy, Beliebers blew all their babysitting money and started beaning him with iPhones ... and his reaction was pretty priceless.