rather than taking your question literally and responding with a flippant remark, I'll try to share some thoughts!
(rdhd's response did make me chuckle though - just imagine if nobody had responded to your thread?! It's enough to make you weep!)
It certainly can be an awful feeling when you are ignored, obviously not the worst thing that could happen to someone or the worst feeling that exists in the world, but in the context of all the feelings a person has felt in their lifetime, it could conceivably be the worst feeling they've experienced to date and, at the time that they are experiencing it, it can feel like the worst feeling in the world.
I guess there are many reasons for ignoring someone - sometimes it's justified and is used as a tool to get a point across, other times it's not justified, but still not necessarily intentional or deliberately nasty either - it can happen as a result of the other persons cowardice, shallowness, indecision, selfishness, lack of awareness, lack of compassion, fluctuating prioroties etc - the list is endless really.
But it can certainly leave the other person hurt, self-doubting, confused, sad, lonely etc - again, the list is endless.
Sometimes mutual ignoring between two people can strengthen the relationship and provide thinking space - 'absence makes the heart grow fonder'.
Other times if someone's ignoring you it can be a sign that you're actually better off with them ignoring you.
When I was growing up, constantly arguing with my Sister, I was always told to ignore her when she was winding me up - it's fair to say it would usually work to an extent, winding her up far more effectively than retaliating, so probably a crappy feeling for her, but didn't provide me with any real outlet for my feelings. A one-way argument is not an argument.
That's a very different type of ignoring to that of someone who blatantly ignores someone, particularly in front of others - for example a group of people sitting around together discussing what to do at the weekend...one person comes up with an idea and asks everyone if they're free...except for one person.
I was at badminton training on Friday, mid conversation with someone and as soon as a court became free to play on, the person I was speaking to just broke off and started arranging a game - I wasn't excluded/ignored in terms of the game itself, but the subject I was talking about was sudddenly ignored in favour of this other distraction - I was a bit put-out, but I have a feeling I'm inclined to do the same to others sometimes.
Generally, I think ignoring people - decent people, with genuine decent behaviour - is not a good quality, but there are times when it can certainly be justfied
Cheers
TTG