Fun story. I was tasked with figuring out a connection problem on a client's network. STP was enabled, but everyone having problems were all connected to one switch.

Some investigation later and STP's root port is not the expected root port....

After some investigation, a user took the ethernet cable for their computer (Daisy chained off their VoIP phone), and decided to store it, in the wall jack.... Across the office.

That was Jack was on a different switch, and it had a lower port cost than the primary root port between the switches, so naturally, let's send all inter-switch traffic over to this..... Telephone.

/Facepalm