Haley, who was the head coach in Kansas City for two-plus seasons before being fired in 2011, wrote "Chiefs suck!" while he was in a hotel bar the night before the Steelers' home opener.
A picture of the napkin appeared on Deadspin.com along with a story written off an email sent by the fan.
"It was no disrespect to the Chiefs," Haley said Thursday. "I wrote what I did in jest. I've never at any time said anything negative about the team that gave me a chance to be a head coach. It was between myself and the [fan], and we laughed. That was it. There was no other incident."
Haley has endured his share of criticism since the Steelers managed fewer than 200 yards of total offense in a 17-9 loss to the Tennessee Titans on Sunday. He expected to answer questions Thursday about the offense's problems and how the Steelers can rectify them before Monday night's road game against the Cincinnati Bengals.
But Haley also had to address what he called a non-issue after practice.
Haley said he and his family are living in a Pittsburgh hotel until they close on the house they are buying. Haley said he and his wife went down to the hotel bar for appetizers Saturday night when a fan approached him and asked for an autograph.
The man told him he was a big Steelers fan, Haley said, and then said he was actually a Chiefs fans after Haley had signed.
Haley said nothing happened beyond that.
"I wrote something about my former team that I probably shouldn't, so there was no incident," said Haley, who is in his second season as the Steelers' offensive coordinator. "I was very surprised when I came to work this morning that it was an issue."