Please do.
This goes for both guys and gals. But to save some energy, I’m just going to assume that you’re a straight male and choose pronouns accordingly.
So you’ve been friendly with a girl, and she seems pretty cool, but you’re beginning to suspect that she wants to be more than just friends, and you just aren’t interested. Do the girl a favor and put her out of her misery. The sooner you do it, the less awkward it’ll be. And don’t wait until she spills her guts all over your shoes.* I’m talking preemptive strike. If she asks you if you want to hang out sometime, well, there’s your opportunity. In as light and casual a manner as possible, accept her invitation but confirm that you’re just going as friends, that it’s not a date or anything (ha ha). If you were right about her interest, she’ll probably be a bit flustered but doesn’t want things to be awkward any more than you do and will probably laugh it off to save face. If you’re wrong, great! It’s better to be safe than sorry, right? Either way, if she’s got any kind of brains, she’ll appreciate that you’re a nice and straightforward guy.
Now, if you’ve caught yourself a really shy one,** then finding an opportunity to definitively crush her heart is probably not the way to go, as she’s never going to act on her impulse to confess her undying adoration.*** Instead, just be aware of your behavior around her. Try not to make eye contact with her too frequently. Avoid standing or sitting next to her. Don’t initiate conversations with her. If you become involved in conversation with her, be cordial, but do not appear too interested. If she gets really brave and attempts to engage you in conversation online, reply in a friendly but terse manner and make your escape as soon as possible. Hopefully she’ll get the message. Whether or not you are successful in your attempts to ward her off, her affection will fade with time- these techniques are just intended to expedite the process.
Now get out there and break some hearts!
*For the love of God, not mandals. You and I both know you’re not getting any ass wearing those things.
**symptoms: Gazing longingly from a distance and averting her eyes when you happen to catch her, clamming up and turning strange colors in your presence, and- if she’s really bold- sitting near you so she can pretend not to be gazing longingly up close. Watch out, boys- you may think of yourself as utterly undesirable (you may, in fact, be utterly undesirable), but there’s probably some stranger out there who’s attracted to you. Never underestimate the power of Berkeley vision.
***But no guarantees she won’t chloroform you and take her back to her place.

http://www.urbandictionary.com/define.php?term=mandals
So you like this person and want to spend time with them. So you… um.. well… you hadn’t thought that far yet.
It has been decided that crossing the legs above the knee is feminine and not attractive. Guys, don’t do it. Period.