A large part of my job involves the care and feeding of Purchase Orders.
These documents go by the short form PO.
The correct use of the term would be me composing an email which says "I am forwarding you the POs we discussed earlier."
However, my computer auto corrects POs to Pos.
I do not handle 'pos', I handle POs.
So unless I want to go back and correct every use of the term, the only way to type it without backtracking is to insert a completely incorrect and aggravating possessive apostrophe. The fact that my computer will not let me write the word properly is like nails on an chalkboard - and it happens several dozen times a day.
My colleagues wonder why I growl at my computer? It's because I've forced to write 'PO's' for the 30th time that day.