I like the sentence, "Kissing a smoker is like licking an ash tray".  Actually this sentence is from a book called  Is Kissing a Girl Who Smokes Like Licking an Ashtray? by Randy Powell (1992, Farrar, Straus, Giroux, New York, 199 pages, FIC POW), and later the sentence became very famous.

Suddenly when you think of the sentence "Kissing a smoker is like licking an ash tray", you will feel like laughing. Well, like statutory warning in cigar boxes, we can say this as a friendly warning.

Update :  I was previewing this blog, and I laughed by reading the sentence. And my Project Manager, who sit besides, asked  me for what I laughed ??.... Well he is a smoker, I can't just say this to him now, since some more people are there. Im just waiting for them to move. ;)