When and how should you tell a new guy in your life that you are a woman who ejaculates? I have had some guys get really upset with me in the past, and this makes me feel dirty and unattractive. So I know I need to somehow warn them or something, but when you haven't even had sex with a guy, how do you start revealing such intimate details? That feels very awkward to me. I like sex to be spontaneous. If I start talking about how I squirt when I come, will he be turned off, or will he feel that I am assuming way too much?
I agree with you that premature disclosure wouldn't work very well. But there is usually a point at which it becomes clear that sex is going to happen. Bring up your bonus feature of ejaculation around the same time you are making it clear that he needs to use a condom.
I'm fond of women who ejaculate, but I don't like to be surprised. A soaking-wet mattress is a big turn-off. So be prepared. If you're going to be having sex at your place, put a plastic sheet on the bed with a soft sheet over that, and have some changing pads handy. These can be bought at any drugstore. One side resembles fabric, and the other has a waterproof coating. Get a few hand towels as well, and keep a small stack of those handy alongside your lube, condoms, and any sex toys you might need. The changing pads are not bulky, so you can fold a couple into your purse (as long as it's not a teeny tiny clutch) if you'd rather go to his place.
Some guys will not believe you or will never have heard of female ejaculation. Some alternative expressions are: "I get really, really wet when I come, and the fluid escapes under pressure" or "I get so excited when I come that the juices literally squirt out of me." Tell it like a giggly, exciting, but slightly embarrassing secret, and he will probably think you're being very cute.
The single biggest fear guys have about female ejaculation is that you are losing control over your bladder and peeing on them. If that comes up, explain that this is something that a certain number of women do; there's been research on it; the fluid is not urine; it doesn't smell or taste like urine; it just means you are (meaning he is) a really good lover. Implying that this only happens if his cock is extra-big or just the right shape or he fucks in an especially effective way won't hurt.
No matter how awkward the conversation might be, you do need to have one. If he's going to wrinkle his nose and get too freaked out to have sex with you, well, that's hurtful. But it hurts less to be rejected during a preliminary sex negotiation than it does to get rejected after or during the sex act itself! You can increase your odds for acceptance by doing a little personality assessment before you come out as a female ejaculator. Look for guys who seem open-minded, relaxed, flexible, and curious about sex. If he's got a rigid personality or seems obsessive-compulsive about his personal hygiene, you might want to look for another trick.