A Sweet Puff is a small glass water pipe (bong) used to smoke Methamphetamine (ice) Amphetamine (Speed) or Crack cocaine. Commonly used as a verb by those who have not had the required education to realise it is a proper noun i.e people who smoke from sweet puff's.
Jason: Hey bro what are you doin'?
Stevo: Havin' a sweet puff bro.
Jason: Havin' a schweet puff!