Hi all,
I have just bought a pair of Nikon 10x42s and they are the first pair of bins I have had that come with a rain guard. I was quite excited by this but now that they are attached - what a pain!! Every time I go to look at some interesting little fella lurking in the bushes I get a mouthfull of plastic, or a nip in the chin or a scrape on the cheek. HOW are these things supposed to work? Are you a rainguard 'on' or a rainguard 'off' kinda birder?
Andrew
The plastic in the face thing is a pain, as is the "I can't see anything, oops the guard is still on" moment. But bear with it - rainguards are very useful.
As well as protecting your fab new bins from rain, you'll also find they work for soft drinks, pasty / sandwich crumbs and inadvertant thumbs.
Yeah, know that one!
I've found that it helps if you make sure that the 'thin' bits of the strap (I'm assuming you got a wide, 'camera' type strap with the bins?) are long enough to allow you to move the rainguard far enough up them to miss your chin when you're using the bins 
Try positioning the plastic adjustment clip thingies (what are they called?) as close to the wide part as possible.
Persevere with them though, as mine have stopped all sorts of rubbish getting on the eyepieces