Warning! This is only a concept, 3D printed plastic is not fire proof and I accept no responsibility for injury caused by this cotton bud gun.
I printed this as proof of concept, it uses a mini hob lighter (available on EBay) to launch a cotton bud (ear swab) cut in half and put down the barrel cotton end first (slightly dampened). I printed the chamber separate to ensure no supporting structure was inside, before gluing it to the bottom of the gun using PVC Pipe Cement (type used by a plummer). The barrel may print with support, I used a thin screwdriver to push this out.
When the glue is was dried, I put the half ear swab cotton end first (after a little lick) in the barrel, put the lighter in the chamber hole, carefully squeezed the trigger for about 8 seconds to let some gas in (not all the way as to light the lighter), then aimed and squeezed the trigger all the way in to activate the piezoelectric ignition.