A prominent far-right leader who dismissed the Nazi era as mere bird poop on Germany’s 1,000-year history was swimming in a lake near his house one evening recently, when a man on the shore grabbed his clothes.

The thief’s parting words: “Nazis don’t need bathing fun!”

By the time the far-right politician, Alexander Gauland, a co-leader of the Alternative for Germany party, known as AfD, made it out of the water, the man had made off with the bundle and someone had already called the police.

The episode unleashed plenty of schadenfreude, and some criticism, on social media. Images of a dripping Mr. Gauland being escorted back to his house while wearing only a colorful pair of patterned swimming shorts spread rapidly, and a hashtag was born: #bathingfun.

Mr. Gauland told the Märkische Allgemeine, a local newspaper based in his hometown, Potsdam, which first reported the theft on Tuesday, “My belongings were stolen by someone as I was in the water, and other swimmers called the police without asking me.”