This one's like a playground dare gone too far...
Look your friend dead in the eye and with a straight face, announce that you're going to put a cigarette out of your tongue. And then you do it!
No slight of hand, no switches, no copping out: you actually put a cigarette out of your tongue.
To minimize the chances of getting burned, you lightly and quickly, dab the cigar on your tongue in different places each time. The moisture on your tongue prevents burning, and repeatedly moving to another place ensures no one spot on your tongue gets too warm.