"Head Glitching" is not a glitch.
Its a by-product of map design. Sure gun barrels stick out below the eye line magically and thin metal trash cans can reject any round, FMJ or not but its the way the game was designed.
Everyone uses the cover points, many that cause people to yell out "Head Glitcher!"
What they mean is "I really wish you were more visible so you would be dead instead of me".
Thank you, please drive through.
Whether it's intentional or not (because of how the first person view is, a lot of people may not even realize they're actually "head glitching"; it'll only be seen through the opposing player's point of view), whether people like it or not, everyone will/has head glitched multiple times. As mentioned, it's pretty much map design.