I was in a couple. The first was during an operation in mid 1967 when our CO split the company in two. One group went one way - the second group went another. Unfortunately the second group made a wrong turn and wandered back near us....across some swamp areas. They saw moment across - probably a few hundred meters and opened fire. We knew who was firing at us so we didn't return fire....finally got someone of the radio to tell them to cease. No one hurt but it was close.
The second was when my platoon was providing security for an Engineering company south of Saigon. I forget what it was they were building - a new base camp I believe. Anyway someone forgot to tell the Engineers that we would be out beyond their perimeter. So the first night one of the Engineers spotted us and opened fire. It probably lasted a few minutes until communications was made. No problems after that.
Sometimes you are just in the wrong place at the wrong time. I was on a patrol making our way through some light jungle - again - south of Saigon. The terrain was very flat with patches of jungle that would border these open areas. I think there was probably about 10 of us - we stepped out from this patch of jungle and started crossing the open area. Just as we moved out several Huey gunships passed over us - maybe at 700 - 800 feet. At first I thought they didn't see us. But they flew about 1/2 a mile beyond and then started turning back towards us....lining up one behind the other. The first impulse was to start running - but we stopped moving, faced the Hueys with our hands up in the air....holding our weapons up so the Huey pilots could see what we were carrying. Luckily there were no trigger happy individuals on board. They flew over us to check us out, turned, and went back on there way. The funny thing was it was no ones fault. We were where we were supposed to be. Just bad communications.
I have always been surprised that there are not more incidents of friendly fire deaths. All it takes is a lapse of attention, the wrong move, and a little carelessness.