A busman's holiday is a holiday spent doing the same things as one normally does at work.
Examples of use:
1. I'm a plumber and I spent all weekend putting in a new shower at home – a real busman's holiday!
2. The taxi driver went to Crete with his family and spent most of his time driving them around to see the sights. It was more of a busman's holiday for him than a real break from work!
Image by Gene Hunt on Flickr