When someone inhales smoke incorrectly (be it tobacco or something else), and subsequently chokes.
Boy 1: *smokes + coughs*
Boy 2: dude you just mcglynned it!

or

Boy 1: why is that guy coughing?
Boy 2: because he just failed to smoke so he's mcglynning it
by ibpro November 18, 2010
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When you try to inhale any type of smoke properly and fail resulting in a coughing fit.
Guy1: Wow she's coughing at lot, is she ok?
Guy2: She's fine, she just McGlynned her fag

or

Guy1: Can i have a toke of that?
Guy2: Only if you don't McGlynn it, there isn't much left

or

Guy1: Can i scrape a fag?
Guy2: Nah, you're always wasting them by Mcglynning it!
by DI Girl November 18, 2010
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