OAKLAND, Calif.—Ronnie Reyes unwrapped a Christmas gift from his cousin a few years ago and found something unusual inside: an official Golden State Warriors toaster.

The only problem was that Mr. Reyes didn’t need a Warriors toaster. He already had one. A toaster with the NBA team’s logo was sitting in the kitchen of his family’s home because, as it turned out, Mr. Reyes had bought the same present for his sister the year before.

“What am I going to do with two toasters?” he thought.

It took him several months to come up with a plan, but eventually Mr. Reyes thought of a way to put this second toaster to good use: He started asking the Warriors to autograph it.

He had been collecting signatures for years when he went to a meet-and-greet event in March with Golden State guard Klay Thompson. Mr. Reyes presented him with the toaster. Mr. Thompson stared at the kitchen appliance as if it were an undiscovered species. Mr. Reyes posted a photo of his reaction online that caught fire and has been seen by millions of people.