How come your six pack comes and dissapears?

It depends on the time frame.

If you mean, say over a few months, you can often put on weight, or do a little less exercise and things, not exercise the right muscles, it often goes.

If you mean, sometimes you lift up your shirt and it doesn't look the same, it more than likely is caused by your diet, and what exercise you have recently done.

Because if you've done exercise that uses the abdominal muscles, then more than likely it will be more defined because of increased blood flow to the muscles, which tensen and expand.

It also could be your diet or what your drink. Dehydration causes the skin to be less flaccid, and therefore makes the muscles appear bigger. Often it is something professional body builders do before a photoshoot, so they seem more bulky.

Or food too, one of the most basic things would be obvious is that after a meal, you've got a lot of food in you, and you won't have as seemly muscular abs.

Or your diet as a whole, such as eating proteins or things that would make muscles seem more shapely.

Everybody has a six pac basically even if they are overweight.You six pac disspears our becomes less defined as your body fat percentage increases.To keep you six pac on show your body fat percentage has to be less then 12%.If you slow down your metabolism by skipping a meal or not doing exercise or over eating on your calories l then your abs will fade as your body fat percentage increases.

I had a six pack once, then I drank it and it disappeared

Thirst!