I think Codeforces should add a new tag to the problemset called corner cases for problems that have many corner cases or many participants FSTed or got hacked on. This can let other people know they should check their codes carefully before submitting.

Examples: 1801B - Buying gifts and 1811F - Is It Flower?

You can write some of the problems you got hacked on in the comments, and I'd like to try them.