The one where OneDrive moves all your data to the cloud without asking, then warns you you’re running out of cloud storage space, and when you then disable it, it deletes your stuff from the cloud without moving it back to your disk.
That one’s good fun for the whole family!

Or the one where OneDrive in its default config uploads your Documents folder to the cloud.
And Outlook 2019 in its default configuration stores the .pst file containing your e-mails in the Documents folder.
And Outlook .pst files get corrupted when you access them from inside OneDrive.
So a default MS Office install can corrupt your e-mails if you click “yes” on everything Microsoft “recommends”.