I think you need to work on being comfortable with yourself and your sexuality. That is the real root of this question. It isn't so much about what you are wanting to say to someone else, but how you feel leading up to it, then talking about it. That is where your discomfort is.
Because, once you are comfortable with yourself, and who you are, talking to other people about various topics (including sexuality) gets a lot easier. The fear, or discomfort, fades away and you can simply have a conversation.
A great way to work on this is with people you do know, and are comfortable with. Have open discussions. Challenge yourself with topics that might be more sensitive. Talk to that person about being gay, so that you become more accustomed to putting it out there. It takes time, but you will eventually shake off some of those butterflies, and when you decide to talk to a stranger it won't be such of an issue anymore.