Movie legend Eastwood hit headlines after his bizarre performance in Tampa, Florida last Thursday (30Aug12), during which the Dirty Harry star chatted to an invisible Obama about foreign policy and economics, suggesting it was time for the President to be replaced by his party's candidate, Mitt Romney.
His eyebrow-raising antics provided great material for Penn, who is now a member of the leader's White House Office of Public Engagement, and he took the opportunity as one of the main speakers on the first night of the Democratic National Convention in Charlotte, North Carolina to mock the film veteran.
Praising Obama for his successes during his first term in office, the Harold & Kumar Go To White Castle star said, "I've worked on a lot of fun movies, but my favourite job was having a boss who gave the order to take out (terrorist Osama) Bin Laden and who's cool with all of us getting gay married (sic).
"So thank you invisible man in the chair, for that, and for giving my friends access to affordable health insurance and doubling funding for the Pell Grant (government funding for financially-strapped students)."
Penn's appearance took place shortly before First Lady Michelle Obama took to the podium to speak to campaigners.
Black Eyed Peas star will.i.am and actress Eva Longoria were among the Democrat supporters in the audience, while Glee actress Amber Riley performed the American National Anthem at the political event.