"Everyone is predicting a nasty election, and we have all agreed that families are off-limits," Obama said. "Dogs are apparently fair game."
Obama then introduced an "ad" from a fake Super PAC that "frankly, I think crossed the line."
"I know Governor Romney says he has no control over what his super PACs do, but can we show the ad?" Obama said.
What followed was a video featuring the story of Seamus Romney -- the GOP hopeful's former pet Irish setter who was once strapped to the roof of the Romney car for a 12-hour road trip.
"What about President Obama? Under his leadership, man's best friend has been forced into automobiles," the fake ad said. "Imagine the European-style socialism that he has planned for the next four years. More government handouts, a life of government dependencies, indoctrinating our children, a left wing social agenda, a leading from behind. America's dogs cannot afford four more years of Obama. That is 28 years for them. They need leadership now."
As the video ended, Obama joked about criticism he's received in recent days over eating dog meat when he was a little boy in Indonesia, an incident he wrote about in his book, Dreams From My Father.
"That is pretty rough, but I cannot take it, because my step-father always told me it is a boy-eat-dog world out there."
Host Jimmy Kimmel -- who spoke after Obama -- also threw in a dog joke, directing a bit of advice at Uggie the Dog, a WHCD attendee and star of the Oscar-winning "The Artist."
"If Romney ever asks you to go for a ride, call shotgun," Kimmel joked.