Talk about sticking out like a sore thumb.

A campaign flier distributed to promote Bill Thompson’s campaign for mayor includes a passerby in the background flipping the bird at the camera.

The unnamed man is sticking his middle finger out as the mayoral contender is shown warmly gripping the hand of a young girl while a crowd of his backers carrying blue campaign signs walk behind him.

One source close to the Thompson campaign claimed the accidental photo-bomber was merely hitching up his shades — though it certainly appears that he had other intentions in mind.

The ad was paid for by United For the Future, a Political Action Committee spearheaded by the teacher’s union, which has endorsed Thompson.

It’s not yet clear how many of the fliers were distributed.

A Thompson spokesman said the campaign did not generate the flier, which hit mailboxes this week.