知らんけど means “…but what do I know”. Kansai speakers add 知らんけど (“though I don’t know”) at the end of a confident statement, to dodge responsibility with a wink.
Is 知らんけど rude? Who can you say it to?
With friends: OK. With coworkers: avoid. With a boss or teacher: avoid. Kansai, jokey. Tacked on after a confident claim.
How common is 知らんけど in real speech?
In 1,905 live comedy routines, 知らんけど appears in 38 lines from 22 comedians.