Can you...

I've never tried.  It looks like something I would fail at.

Easy stuff.

Been doing it for years. Makes restarts at traffic lights a lot easier.

I've been getting better and better at it and looking forward to being able to pull one off at a fresh red light, then green arrow, then go time. I'm more 30 seconds at a four way capable right now. 

Practice indoors on carpet.

I'm carpet free

HA!!!  So are we except for the workout room......there have been many bike crashes there from track standing and rollers.

Haha! I live life dangerously and just practice on the road. "Taste death, live life"

HAHA!

An old hunting partner used to say, "I came into this world kicking and screaming and covered in someone else's blood....I have no problem going out the same way".

I have an unfair advantage. BMX racer since the age of 8. But I learned without a gate by balancing in the driveway. Face upward and use the slope to push you back. Then just put enough pressure on the front pedal to make you rock back and forth. By rocking I mean move less than an inch. You can use your inner leg to push on the top tube if you feel like you're falling to one side. You'll eventually not need the top tube and then the slope will be unnecessary. Your front brakes become the slope/gate. A fixie is much easier than a freewheel bike. Track stands help a lot when you're stopped at a red light.

The key is to remain relaxed. As soon as you tense up, you'll fall over.

At stop lights I still hear the old call in my head (Riders up. Watch the gate. Beep, beep, beep, beeeeeep). Any BMXer will get it.

Well, I don't know that I CAN'T do it.  I like to assume I'd be boss at it.

I can for a few seconds....but those few seconds are done like a BOSS!

the ensuing few seconds are not quite so awesome to be honest :-)

now I do what's known as a semi-trackstand. 

Oh....wait....i didn't know we were talknign about being BOSS.  That only truly happens when you are at a red light, you fall over, and your face is pressed against the window of the car you were next to.

Which further justifies my response

I can for a bit, but this is actually a reason I don't do it. I don't want people wondering what I'm doing. Intention should be easy to see, so take my foot out and put it down. Times I might are if I'm expecting to go again rather quickly. A light is just about to change, or some situations with stop signs and cross traffic.

This is me as well.  Unless on a slight incline, I always need to be inching forward.  I use it if I know the light will change within the next 10 seconds or so, but I won't do it just to do it...especially if in a group ride with other riders who don't also track stand.  

I also commute a lot, and as Ben mentioned, it's important to be predictable for drivers.  When you start turning your front wheel 45 degrees one direction to balance...cars may think you are intending to turn.  If they see you doing it for 20+ seconds, they may get the idea of what you're doing, but the first 3-5 seconds most cars will think you're trying to turn in front of them or something.  Most of the time it shouldn't be a big deal, but clipping in and out isn't that big a deal either.

The key is being able to wave the cars through while you're stationary.

That's why you practice track stands with one hand as well as two hands.........I'm serious.  If you can't let go with one hand, I wouldn't even think about doing it in traffic.

Yep. I do it at the track. Check out this race: Marymoor crawl.