Weird bruise thing behind knee

So I was trying on some bike shorts this afternoon and was looking at myself in the dressing room mirror and I noticed a purplish dot on the back of my knee. It's the color of a bad bruise, and fairly small. It feels a little twingy but not painful. The skin over it looks good, it's definitely subcutaneous showing through. It's in the "dimple" at the back of the knee joint.

It's in a hard to see spot without a mirror so it might have shown up days ago for all that I know. I did so some harder than usual riding a few days ago, could that have caused it?

Any ideas? Is this a varicose vein?

Attached pic (kindly ignore the stretch marks and the shaving rash, please!)

Could be a blown capillary. I get them (Irish skin--fair). Usually they aren't that big, though. Just red dots, like moles. They aren't anything to worry about, and my doctor told me that as I get older, I'd get more of them. A prediction that is coming true, unfortunately. I did have a larger one on my thigh a few years ago and went to the derm because I thought it might be a melanoma (uneven edges, red in color, etc). She said it was just another blown capillary. Weirdly enough, it went away shortly thereafter.

If I were you, I'd get it looked over by a derm. I can't tell too much from your photo---it might be a mole.

I had something that looked very much like that from a tick bite - found the little sucker attached in almost exactly the same spot, followed all precautions to remove him, and had a place that looked exactly like that for about 2 months (maybe longer) - it did finally go away, though...

Perhaps it's a bite???