I'm Proud of My Prank on That Know-It-All Student

Alright, folks, let me tell you about something I'm really proud of. There's this one student in my class who thinks they know everything and never shuts up. It got to the point where it was affecting other students' learning time, but I couldn't bring myself to give them detention or send a note home because that would be unfair to their parents. Plus, I didn't want anyone else getting involved, this was my show to run. So, I decided to take matters into my own hands and play a little prank on the kid. One day, I left a Post-it note in the corner of the whiteboard that read: 'If you can answer this math question correctly, all homework will be cancelled for the rest of the year.' Naturally, it was impossible. You should have seen their face when they tried to solve it and realized there wasn't an answer, priceless! And yes, I laughed right along with everyone else during lunch break while my little genius sat at her desk, staring at the board in silence. So here's what I want you guys to tell me: Was I the asshole for doing this? Or was I just doing what any good teacher would do when they've had enough of one kid ruining class time for everyone else? Drop your thoughts and let me know.