Impolite Jokes

[I have been telling this joke in Punjabi (an Indian language)
for about 7 years. It is probably not original, but I haven't come
across it anywhere else, either]
A Muslim and a Sikh were once traveling together in a train.
Both being from Punjab, spoke the same language and had a great time
talking to each other and generally whiling away time. Came lunchtime
and the Muslim took out his lunch and started eating without offering
it to the Sikh. The Sikh was rather insulted at this impolite behavior.
"What city are you from?" he asked the Muslim. "Lahore," replied the
Muslim. At that, the Sikh started cursing the people of Lahore,
mentioning, among other things what impolite &*@##!%%'s they all were.
Being guilty, the Muslim swallowed all this in silence.
A few minutes later, the Sikh was hungry and he took out his
lunch and started eating without offering it to the Muslim. The Muslim
saw this as an opportunity more...