The video, which was widely mocked after it was posted on Wednesday, showed a seemingly nervous O'Rourke before getting the jab. In the video, O'Rourke takes a deep breath and closes his eyes before receiving the vaccination.
After receiving the shot, O'Rourke said "That's it," in a hushed tone. The video was posted to his Instagram, prompting a round of criticism from people on social media.
Many took aim at the size of O'Rourke's arms while joking about his gun confiscation plan.
"At least he's walking the walk and showing he's not in possession of any guns of any kind," one user tweeted.
O'Rourke has a history of offering voters a candid look at his life. The 2020 hopeful has live-streamed himself getting a haircut and going to the dentist. The haircut incident similarly earned him mockery online.
The dentist video, posted in January, showed O'Rourke with his mouth wide open as a hygienist gave him a cleaning.