I've noticed this with Delhiites, HPs and with Arya Samajis; they go to Gurdwara for the free food but make Sardar 12 O'clock jokes and say that KPS Gill was good and Bhindranwale a terrorist. They feel Sikhs are labourers beneath them yet insist Sikhs believe in Rama and we're soley created to protect Hindus.
Many Hindu Punjabis were also involved in the 1984 Delhi genocide and aftermath in Punjab
Shame on Hindu Punjabis and Delhiites
I agree about the sardarji jokes to some extent.
But most such self-deprecatory jokes were created by Sikh writers like Khuswant Singh and others. It is a sign of health, high self-esteem and positivity to laugh at oneself or one's own community without taking offence. Among the Sufis there is Mullah Nasruddin jokes.
In his book President Giani Zail Singh, the Sikh author Joginder Singh states
"...who can enjoy a good joke against himself or against his tribe except a Punjabi and more particularly, a Sikh?"
The Hindus, being a caste-ridden lot, often enjoys jokes at other's or other caste's or religion's expense but will not tolerate one against their person or caste. It is sign of low self-esteem and pettiness. It is the progressive Hindu liberals and secularists in this regard who seem to be an exception to this.