Check this nonsense out.....
http://www.theblaze.com/stories/2013/04/16/decorated-vet-arrested-after-rudely-displaying-his-rifle-says-officer-pulled-gun-on-him-in-front-of-boy-scouts/

I think there may be more to this story after reading many of the comments, such as:

1) Does he have a criminal background or outstanding warrant?
2) Is Texas in fact an open carry state? Some comments say it is a CCW state but not open carry.
3) Why wasn't his rifle slinged to the rear with muzzle pointing down?
4) Did he intentionally ignite the situation, whereas he probably could have easily diffused the situation?

Many other valid comments (didn't read them all) but should be interesting to see what happens when all the facts are sorted out. Whether or not the police officer handled the situation properly or not can be debated but I believe the majority of LEO would be concerned if they came across a guy with an AR in this manner.