1. Greasy foods or Fatty foods do not cause acne.
2. Smoke does not cause acne.
Acne comes from clogged pores and over active sebacious glands.. Dirt may clog a pore and the glands under neath continue to secrete mucus, which then is trapped under the skin.. A bateria colony forms and swells and thus a zit appears.. There isnt all that much we can do about the sebacious gland end of the battle(except hormone like drugs like accutane), so keeping our face clean is the best way to prevent the buildup that causes acne..
For the most part, what you take into your body has nothing to do with this(like pot smoke).. However their are exceptions.. Drugs that cause a stress reaction will make you break out.. When you are under stress, your sebacious glands secrete more than average, making breakouts easier to occur,, Really, stimulants are the only drugs that cause a stress like reaction)plus they make you touch your face, putting more dirt in your pores).
In other words, pot should not make you break out. Not keeping you face clean, combined with hormones and genetics will.