A Junk egg is an egg with an N in it. All eggs of the same type have the same name. IE "dragon egg" could be junk or not. You have to have someone else wish list the egg and search to see if there are a lot of them up for trade. Don't just let anyone search your eggs, they might say it is junk when it is not.
I seen it many times by top players even.
Also note that every egg is actually a different monster based one what is inside it. So if you see a trade up for an egg and it will nottake yours, they are looking for a different egg.
Hypno kitty will make you feel better..... and make you trade me everything, ma ha ha ha. :-).