I was talking to someone who was complaining that her husband had a nickname for a co-worker. She was extremely uncomfortable with that and I understand why. Nicknames are ways of showing affection for people and so I tend to agree that it pushes the boundaries more than a little bit.
Here is the deal. You may think it’s totally fine. And that’s fine. However, if your spouse is uncomfortable with this or anything, then don’t do it. The point is not whether having a nickname for someone is wrong or not. The point is that we don’t want to continue to do things that make our spouse uncomfortable.