I train an unique martial art (it's local;)) for about 3-6 hours a week in the dojo, from time to time I take over a training. When new people come in I show them around and teach them the basics that sort of thing.
Here's what I do, I tell a girl I teach self defense to children and women.
Which well....isn't a lie.
It's just a more subtle way of saying you are in to fighting.
On top of that you get awarded the 'Leader of Men'-medallion as well.
Now in the club this often leads to 2 situations:
a) Oh cool, can you show me something?
Just act like you didn't hear what they say and go for the takedown while she is repeating herself:p
b) Wow, that's awesome....I'm a gymnast (or whatever) and do teaching too!
She's trying to find some common ground to talk about....
....yeah teaching is so rewarding (Conversation often goes dull though, havent found a solution for that)
When a girl is over at your place or whatever, you could just bring your ground game, assuming you have any

Just keep things funny and don't get too touchy from the start.
I train a lot and well it's one of the few things in life I can really be passionate about. I feel no need to hide it. From time to time I find myself in a position where a girl wants to go running with me or escort me on her bike while I'm doing my roadwork. Sure you aren't at your prettiest with a face as red as a tomato, sweat dripping down your balls, but it's running what did she expect?
And well if a girl wants to go with you well:p then you basically have this one in the bag already:lol:
Haven't read anything but the top comment this time;) Don't hate me for it.