Solved the whatizzit !
I finally know! It's been a source of curiosity for the last few days and I finally have an answer. Not to "what is the Supreme Question to which the answer is 42", but what "Yaara da tashan" means.
Aamir Khan's Coca Cola ad with him doing the Punjabi farmer signs off with that extremely vernacular line and it had been mystifying for a lot of us. But thanks to a guy called Kamlesh (no mean "Punjabbee" accenter himself), we found out that tashan is sort of slang for "style". So what Aamir Khan the farmer means to say in response to "Tussi great ho" is "Yeah baby! That's my cool style" (or words to that effect in Punjabi of course).
I can go back to worrying about the world now that that thread is tied up.