I too have a hard time flirting with my own husband, how silly is that. It is all this darn baggage and not necessarily that he does or doesn't enjoy it.
I do, however, flirt with him in email because I am not there to put my own spin on what his reaction (or lack of) was. Also, he can then process the flirt and figure out how to respond. I think with my H that he just needs time to process the flirt and respond in kind. If he doesn't have this 'time', he will sometimes say or do something slightly negative even though he may have secretly enjoyed it. He is not great with social skills and I believe I have misinterpreted this for YEARS as him being uninterested in me. Now! If I could just remember this at the time that I do occasionally screw up my courage and get a nonreaction, I'd be in business. I've also found that the more I keep my emotions under control and don't pull back from the nonreactions, the more he pushes himself to give his true reaction.
