My tone wasn't harsh in my original post (noted by the lol's and smiley faces), no need to really relax. I'm just pointing out the lack of attention to detail. If you want to call your AR15 with a 16" pencil barrel, A2 stock, and flip up front site an "M4", go right ahead. Just expect the raised eyebrows from many.
Again, no one is suggesting it needs to be 'issued from Uncle Sam'.
I'd feel the same way if someone haphazardly slapped a Stingray emblem on their 1969 Corvette for nostalgic reasons, but didn't at least install the correct hood.
Like you've eluded to...just call them all AR-15's if one doesn't know the differences. Problem solved. :)