Ok, stupid question, but as I was cleaning and reloading mags last night I had this thought, Anyone ever heard of a person trying to shoot 5.45x39 in a .223 or 5.56 chambered gun, and what happened! Just curiosity!

Not an issue.
5.45x39 will not fit into a 5.56 bolt face, so the round won't chamber successfully.  
5.56x45 is too long to fit in a 5.45x39 chamber, so it won't chamber successfully.

Yup. Was in a carbine class over the summer. Guy got a box of 5.45 mixed with his 5.56. First round stopped the gun hard. I had to go get my range rod to clear it.

ETA: The round did NOT fire.  It wouldn't even chamber, but we couldn't get it out with the normal clearing procedures.  Had to pound it out with a cleaning rod.

I would think it may chamber but swell hard if fired and not extract . supposedly you can use .222 brass to make .5.45 cases . I would think the case head should be close

Nope.  The case head of 5.45 will not fit into a 5.56 bolt face.  Therefore it's not touching the bolt face and the firing pin can't reach the primer.

5.56 will fit into the bolt face of a 5.45 bolt, but the shoulder will cause the bolt to stop about 1/4" out of battery, so the bolt will not be able get past the barrel extension lugs, so it won't be able to cam closed. With the bolt unable to cam closed, the firing pin cannot reach the bolt face to set off the primer.

The 5.45 round is tapered and wider at the base than a 5.56 round.  If you accidentally load a 5.45 round into a 5.56 rifle, the 5.45 round will wedge tightly into the 5.56 chamber and stop.  It won't fire, but it will be a bitch to get out with out a cleaning rod.