- "Opps! Sorry about that, buddy!"
- Mr. Harkin after going inside the bathroom when Greg was already using the toilet.
Mr. Harkin is a adult who was briefly mentioned and appeared in Diary of a Wimpy Kid: Cabin Fever. When Greg Heffley was four years old, Susan Heffley and Frank Heffley held a cocktail party and Mr. Harkin was invited to it. Harkin wanted to use the bathroom, so he opened the door, but Greg was already there using the toilet. Greg was young and did not know that people are supposed to lock the bathroom while using it. Harkin went away. Greg felt embarrased and went to his parents and told them what had happened.
- Diary of a Wimpy Kid: Cabin Fever (First and only appearance)