"I see that in my nightmares," he said about the photo on Wednesday's "The Ellen DeGeneres Show."
"Your selfie shot was the most spectacular most successful thing, and it worked out so well that it's this horrible dark cloud over my head now," he added. "How do you beat the selfie that broke the Internet?"
DeGeneres comforted the 41-year-old actor, saying, "You can't plan that. I hoped that it would happen. I hoped people would jump in," she said. "So all you have to do is have a nugget of a good idea, and if everybody's on board and they're playing, whatever your idea is, they're with you. That just was such a perfect fluke that happened and I was so lucky."
But the former "How I Met Your Mother" star -- and first-time Oscar host -- is confident nonetheless.
"I'm gonna try and do something better I think," he said.
Harris told Ellen one of the hardest aspects of the writing process is crafting jokes that haven't already been used.
"It's a tricky process with the content," he said. "I'm finding good jokes that we had that are funny and strong, then I'll watch a late-night talk show and they'll say the same joke ... the Grammys, gah! "Saturday Night Live," gah! I just want everyone to stop talking until Monday!"
NPH also stressed the delicate balance between jokes for the nominees and jokes for the audience at home.
"I want to make sure that the people that are in the theater, that are nominated, that are very nervous, enjoy the show and feel respected, like I'm talking to them," he shared. "But I think it's more important -- nay equally important -- to be talking to people at home and making sure that the people, the larger group of people that are watching it at home feel that I'm talking to them and that they're not excluded from the party," he said.
The 87th annual Academy Awards show will air live on ABC Sunday from the Dolby Theatre at the Hollywood & Highland Center at 7 p.m. ET.