I’ve occasionally taken a mouthful of lighter fluid and spit it out past a flame.
Had my father standing-by with a wet towel in case it didn’t go as planned.
It was a trick he’d first seen at Osan.
I’ve done the cigarette lighter flame throwing trick using the gas in the mouth (not lungs) and blowing it out past the flame.
Not hard or particularly dangerous.
We used to suck up a mouthful of butane from those disposable lighters, then blow it through a cigarette while lighting it, it would make a little blue flamethrower, and the cigarette protected you from getting a flame shooting back into your mouth. Not as impressive as the lighter fluid trick, but safer.