My colleague's iMac connects to my MacBook Pro via Bluetooth without my consent & messes things up! So, I'd be using my Magic TrackPad or listening to music via Bluetooth headphones and suddenly the mouse cursor would start jumping around or the Bluetooth audio would start breaking up, and that's when I know that my colleagues iMac has connected to my computer. I go to the Bluetooth menu and I disconnect it. After a little bit or awhile, it connects again...

No one knows how or why this happens.

Could someone please tell me what's going on and how to stop it?

Oh, I forgot to mention, another one of our colleagues also complains about this particular iMac connecting to his MacBook Pro.

Update: immediately after posting this, it happened and I took a screenshot. Here it is 

 

Mahmoud's 27 iMac is the culprit.

Another update: Mahmoud's 27 iMac does not appear in the list of paired devices
I had the exact same issue and the culprit was an app I had installed called MacID, version 1.1. I deleted MacID and the problem went away but supposedly you can upgrade it and fix the issue as well

Reference: https://discussions.apple.com/thread/6702053?tstart=0