Try rotten eggs. That's what the worst cases of bad breath smell like. And if you talk to someone who has it, you know it. However, if you have it, you probably don't know it. There's lots of different kinds of bad breath, according to The Breath Center .
Halitosis is caused by too much sulfur in the mouth.
But there are some obvious clues. Also, people may crinkle up their noses when you are talking to them. If you need more visual proof that you might have a bad case of halitosis, try this technique from California Breath Clinics Wipe the top surface of your tongue with a piece of cotton gauze and smell that. Furthermore, if you notice a yellowish stain on the cotton, it's likely that you have an elevated sulfide production level. Or just lick the back of your hand, let it dry and take a whif.