Peshengwengweng comes from the Latin word peshengweng which means to hover past your waistline at a high speed and the last Weng means The sound a AR15 makes.
Some people even use I tg for slangs
Peshenwengweng was used in the li ate 21st century when an artiste sang a song with that sound. It became a laughing stock hence people say it's an imaginary gun.
Mi gun guh suh peshenwengweng
Fly past yuh face
One inna yuh hardback, mek yuh fly inna di grave