A bad egg is an egg that cannot be hatched, some refer it to a "spoiled egg". You mainly get this if you leave your egg in a PC box for to long. You can also get it by using a hacking code that does not work.
A Togepi.
The best way to get rid of a bad egg is if you have 2 ds's, another ds Pokemon game that you hate and trade the bad egg to that game and there you have it. This is the best way to get rid of a bad egg and P.S. you cannot give a poke'mon an egg.
You should never attempt to hatch a bad egg. Hatching a bed egg, may lead to damaging your save file, or even the game as a whole.
No legendary can lay an egg except for manaphy which gives an egg to phione and you can not get manaphy or phione in heartgold
You get an egg from Professor Elm's assistant from any Poke Mart.
Deposit one of your Pokemon and you may get the egg
yes. at Pokemon day care if they have to same egg group.
evey Pokemon has an egg except legendarys and ditto
You can get the bad egg in the games: ruby, Sapphire, emerald, diamond, pearl, and i think platinum, and possibly heartgold and soulsilver.you have the bad egg when: it hatches like every 2 steps you take. another egg hatches from the egg. you can never deposit your bad egg in your Pokemon storage thingy, because it won't let you, although you can trade with other people. and if you have the bad egg, then your the unluckiest person , because the bad egg will freeze your game, and delete your save file. so all that work you did in your file, will all be deleted.
In HeartGold, give a Mantine the Wave Incense and breed it. The egg with hatch into a Mantyke.
use an action replay it will eventually give you a bad egg. I don't recommend it though being as a bad egg hatching will glitch your game.
put two Pokemon in the daycare 1 female and 1 male