The stereotype has been remarkably stable for a hundred and seventy years: large, loud, brave, generous, hardworking, agricultural, not clever.
It was constructed deliberately. The martial races doctrine described Punjabis in exactly these terms in recruiting handbooks, as a justification for recruiting them and not others, and the description was a policy document before it was a joke.
The Sardar joke, current across India for decades, is the same content in another form.
Punjabis have adopted a good deal of it themselves, which is what usually happens, and the loud generous Punjabi of Hindi cinema is partly self-portrait and partly compliance.
What it leaves out is the entire intellectual history on this site: the scripture, the scholarship, the poetry, the physics, the fibre optics, the constitutional argument and the two hundred years of political organisation.
A region that produced a religion, a state, a grammar, a Nobel laureate and the technology carrying this sentence is understood elsewhere as a place with tall friendly farmers, and that understanding was written by a recruiting officer.
The stereotype is loud, large, hospitable, agricultural, martial and slightly ridiculous, and it is carried by Hindi cinema, by the joke genre and by the diaspora's own self-presentation.
It is flattering and it is confining. A region with a thousand year literary tradition is represented nationally by a dance and a plate of food.
Punjabis participate in it. The performance of Punjabiness abroad and in the media is largely made by Punjabis for a market, which makes the complaint about it complicated.