Depends a bit on the context.
Glorfindel makes a good point in his answer about 'thanks, done, edited' comments too:
There's one caveat: the 'Done' comment might ping the author of the first comment (either directly, or because the only comments are by the author of the post and the author of the first comment); if the comment is deleted before they visit the site again, they might miss the inbox notification. So it's probably better not to flag 'Done' comments too soon after they're created; not everybody is using the new Follow Posts feature.
If I look at the timeline, the comment was posted 23 hours ago, flagged 21 hours ago and I cleared the flag 20 hours ago: Just 3 hours after the comment was posted, which is a rather short time. This was also my main reason to decline the flag: A comment barely 3 hours old might not have been seen and appreciated yet.
Besides that, this comment is made on a answer to a post tagged fun. I'd argue fun is fun, but also falls out of 'usual' quality guidelines like 'compliments that don't add new information', because fun in itself isn't focused on adding new information. So, let's have a bit of fun, and let people say stuff like this. It's quite usual to see remarks like that on fun posts, and I tend to be lenient with them because they're nice and fun, exactly what the post is for.
I would recommend letting fun be fun, and use flags for when fun becomes not fun, instead of using them to lessen fun. Because it's never fun to handle flags asking you to delete fun.