I can only speak to the US, but this didn't stop school administrators - their interpretation was more important than credibility when it came down to decisions made immediately post-Columbine. Parents demanded action from the administrators, even if none was needed, and so administrators needed to demonstrate that they were doing something. Bans on long coats, primarily black outfits, discussing video games, etc. weren't uncommon.

Activities done outside of school that were discussed in school absolutely made it onto this list and would result in suspensions.