In a video shared on the official Twitter handle of his party Pakistan Tehreek-e-Insaf, prime minister Khan is seen sitting while the rest of the world leaders and dignitaries at the event in the Kyrgyz capital stood when head of states of the Shanghai Cooperation Organisation arrived for the opening ceremony.
He stood briefly when his name was announced and then seated himself again before the other leaders, in a breach of protocol.
The cricketer-turned-politician, who has not attended many international summits, was trolled online by the netizens for the seating gaffe after the video went viral.
"Imran Khan again caused national embarrassment at Bishkek, ShanghaiCooperation Organisation. When everyone was standing. He sat, stood when the presenter took his name but sat again. Arrogant, ill mannered, or an idiot?" one Twitter user wrote.
"Must study the decorum of diplomatic visits to make some mark in future Mr Imran Khan," wrote another.
"He came, he sat, he got up, he sat again. Haters gonna say PM Imran Khan has no manners, I'd say he's still handsome," another tweet said.
The video went viral and the Pakistani prime minister was criticised for his "high-handed" attitude.
Earier, Khan broke the diplomatic protocol at the 14th Organisation of Islamic Cooperation (OIC) Summit held in Saudi Arabia earlier this month.
At the sidelines of the OIC Summit, Khan walked away after speaking to Saudi King Salman bin Abdulaziz's translator without waiting for him to translate the message.