What are bida-bida moments you saw that backfired horribly?

As the title says, what are those moments where classmates are being bida-bida but not in a way that is helpful, and it bit them back?

I'm talking about them getting so confident about themselves that their plan just made everything worse.

How did the situation played out? Did you have to step up to fix what they did horribly wrong? Did they learned their lesson?