Smoking, mainly tobacco. When smokers hunch over to light up it looks as if they're performing a service on a small being cupped in their hands. Thus, blowing the elf.

The phrase blowing the elf was coined by a highschool student sick of assholes blowing smoke in her face.
"Dude, don't blow the elf around me, it smells."
by Sara March 30, 2005
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