We all have a fetishist side somewhere inside. Some of us have a kink for office shirts, some of us — for striped knee socks, some — for lace and stockings, and some — for short skirts. And if you have a professional uniform, role-playing when you are semi-dressed (or semi-naked!) is simply unavoidable.
Sex in clothes leaves room for imagination and room for action. You can tease by taking things off and putting them back on. You realize that the rush of desire was so rapid that there was no time to strip!
Your costume does not have to be purposely erotic: a house robe, a construction worker uniform, a suit jacket will do — so that any play will become even more like the real thing.