Tonsil stones, apart from not flossing (which is a similar smell) is one of the most common causes of bad breath. You wouldn't necessarily know you had them. Some people are more likely to get them than others, if you have quite nubbly tonsils, then they attract them more because its a combination of immuno response and calcified food debris that sort of forms them. Its not necessarily do to oral hygeine, by the way - its not because you dont floss or brush or gargle enough, though obviously the more you do that the less you will get them or the less bad they will be. Its more to do with the texture/finish on your tonsils which is purely genetic. So its not your "fault".
One thing that can really help with preventing them and also dislodging existing ones is gargling with aspirin. Bear in mind aspirin is Beta Hydroxy Acid (Salicyilc acid) so an "exfoliant" of sorts, and perfectly safe to gargle with (buy the disolvable kind, obviously, gargle, and either spit or swallow, either is fine). You are then effectively exfoliating your tonsils. If you exfoliate your skin, you are less likely to get pore blockages and spots - well, its sort of the same with tonsils!
They are gross, there is no doubt about that. The sheer amount of bacteria and stuff in the mouth, not to mention the nasal passages, and the fact that tonsils are basically designed to filter out stuff and stop bad infections going down further into your trachea, lungs, etc means that they will sometimes let you down in terms of the shiny nice stakes!!!
Its not your fault, and its very common. What is sad is when someone has them bad and doesn't know, so doesn't do anything about it, and consequently has really rank breath. Having them doesn't necessarily mean you have rank breath - it depends where they are, how big, whether they catch your breath on the way, etc etc.
The poster who said she found a white pellet in her mouth that stank and she spat out, that is definitely a tonsil stone.
Get a torch and have a good look at your tonsils in the mirror - move your tounge around, flatten it, go "arghrrrr" etc and if you can't see any white pustule looking things, you probably don't have them and you can be very happy and smug about the fact!