Kissing

"Top Tips

• If you have to wet your lips before contact, do so surreptitiously. You're about to caress your loved one, you don't want to appear as if you're about to eat them.
• Releasing a fart, sneezing, expectorating, coughing or burping can, of course, seriously impair the kissing experience. It can even ruin a whole relationship.
• No passionate kissing if you have bronchitis.
• Rubbing the nose on the other person's glasses or confusions with other adorning thingies, like piercings can be embarrassing or even painful.
• Don't go out expecting to get snogged if you've got a weeping scabby upper lip brought on by Herpes simplex, otherwise known as the coldsore.
• Biting your lover pops up quite a bit in the Kama Sutra, and quite a few Researchers admitted to liking a little gentle lip biting (both giving and receiving). 'Gently' is most definitely the key word here, no-one wants to have their lower lip bitten off. Gentle nibbling is a more accurate description.
• If you're both wearing train track braces then the last thing you want is tooth-clash... if your teeth clash it means the shrapnel that's adorning your mouth can become impossibly intertwined with the shrapnel adorning your lucky victim's mouth... cue either delicate use of an oxy-acetylene welder or an embarrassing trip to the dentist with your respective parents in tow."
  
  Source
  http://www.bbc.co.uk/dna/h2g2/A848685