Most of the responses have compared keeping your fetish a secret and telling on the first date.
I'll go ahead and suggest an alternative possibility: anyone who would date you should know long before they ever consider dating you.
Allow me to explain.
There is not a day in my life when I am not around people who are talking about sex. Both people I know and people I am just passing by.
Sometimes this is direct, such as about sex they've actually had or about how it's been two months since they last had sex so they really want to have sex.
Other times, this takes the form of references to sex, sex in general, imagery of sex, because sex is undeniably a part of their culture.
Sex is never a secret, because it is the default assumption. Or, what I mean to say is,
"the possibility of someone at some point in their lives wanting to have sex with someone else" is never a secret, because it is the default assumption.
You may take this for granted, but it's worth explicitly pointing it out: people don't have to come out about wanting to have sex. They have to have a discussion about when they want to have sex with a specific person, but the wanting in general is not surprising.
That's two things that non-fetishists have which fetishists don't have:
1) The ability to casually talk about the thing that is your fetish, as both a sexual and non-sexual thing,
and,
2) The ability to not have to talk about the thing that is your fetish, because it is already assumed without you saying anything.
When bringing up your fetish at all seems like an obsession, it is because we don't have those two things.
And so one thing we can do to prevent this perception is to claim those things that other people take for granted, and one of the ways we can claim them is by being open about our fetishes all the time, to everyone we can.
Usually a fetish doesn't get to be a background assumption like sex does, but by being completely open about it, it will be a part of the background information about you.
Then it won't be a surprise if you ever talk about it, and it won't end up being a surprise later if you hardly ever talk about it.
Instead of keeping a secret until the time is right, never let your fetishes be secrets in the first place.
I've been doing this myself for a while now - letting my fetish be background information about me - so I'll say how I went about it.
When I got tired of the double standard where everybody else could talk about their interests all the time and mine was expected to be a secret, I went down to the craft store and got some cord and a pack of beads with letters on them.
I used the beads to make myself a pair of bracelets. On my left arm, the bracelet spells out "FETISHIST". On my right arm, it says, somewhat sappily, "SLIME - PIE - LOVE - WAM". (I'll attach a picture of them to this post.)
And then I just started wearing them any time I went out. I didn't have to directly talk about my fetish; I didn't have to bring it up, though I could if I wanted to. All I did was let it be background information for people to notice and accept.
And as I spent time around my friends like usual, eventually they each would notice what it said. And when I'd meet someone new, eventually they would notice what it said.
Some people would tilt their heads over to read the letters, get a confused look on their face momentarily, and then go back to the conversation like normal.
Some people would ask what my fetish was. Sometimes I simply tell them "messy things" and list some substances as examples. Sometimes I tell them the abbreviation and tell them they can look it up if they want. Sometimes I give them the whole explanation about why I choose to be open about my fetish.
And I can tell you - I haven't lost a single friend since I started wearing my bracelets. Most people take it in stride. Some probably don't understand why I put my fetish out there, but they don't avoid me because of it.
The "don't keep it a secret" approach has many of the same benefits as the "keep it a secret" approach. In both cases, the people around you still get to know you as you, as the regular person you are everyday. They see you as you are, and see that you just happen to be a fetishist.
The only friendships you would miss out on are those with people who are scared away by even the mention of fetishism. I can't say that no one will have that reaction, though the people I know haven't had that reaction.
I do think that anyone who would have so adverse a reaction that they wouldn't even want to know a fetishist - probably isn't at a good point in their life to be friends with a fetishist or to be in a relationship with a fetishist. They may change their mind over time, and if so, that's great. If knowing you helps someone change their mind, that's great. But you aren't personally responsible for changing everyone's mind at your own expense.
Even someone who has a strong belief that fetishes should be secrets should be able to respect you enough to accept your decision to be open. If not, you deserve a better friend anyway.
Now, even though I'm suggesting the possibility of being open about your fetish - you know your own situation better than anyone else. If you think it would get you in too much trouble, maybe it isn't the solution for you, or maybe you'd need to be more selective about the situations you are open in. For now, I personally choose not to risk wearing my bracelets on the job or around family, even though it wouldn't be the end of the world if they found out.
And even though I chose to make something to wear as my way of being open, something different might work for you. An accessory is useful in that you don't have to directly bring up the topic, but casually telling a group of your friends, or something else, could work as well to let your fetish be a piece of background information in the way most people take for granted.