At a nationally televised news conference where he abruptly announced his resignation on Monday, Fukuda was criticized by a reporter for not having had his heart in his job.
"I can see myself objectively. I'm not like you." he snapped back.
The flash of anger took many voters by surprise because Fukuda had kept his testy temperament under wraps as leader.
The comment, the talk of Internet chat rooms, has spawned T-shirts, mugs and even baby romper suits printed with the words: "I'm not like you".
Some voters thought Fukuda sounded arrogant, while others said the leader, who reportedly had not told his wife about quitting, had merely showed his human side.
"It was his last news conference, so he let his emotions slip," said Hiroshi Fukada, 56, a public servant. "Even I feel like saying 'I'm not like you' to people sometimes."
"I like my fried eggs with soy sauce. I'm not like you." said a netfriend.
"I can marry with a man that I love. I am not like you." said one.
"I like dig nose, I am not like you!" said one.
"I come here to do push-up, I am not like you!"