Abercrombie & Fitch is a clothing line that develops clothing materials that say Abercrombie on them. For some reason they think they have been around since the late 1800s, but no one can prove that, so they continue to lie about it and say it's true.
Abercrappie is just the other name for Abercrombie.
Fitch is the other name that people don't like quite as much, so Abercrombie got the majority of it.
Abercrombie, apparently around since the 1800s, was invented by Hollicrombie & the American Itch, two entrepeneurs who went around selling their grandma's clothing that she had knitted for them and they hadn't wanted.
To be honest, Hollicrombie and the American Itch were kind of geeky, as they were losers in highschool and sucked at all the sports they tried out. It wasn't until they were in their late 20's that they decided that enough was enough.
And so they created their own company, and that was that.
Since people wear Abercrombie so much, people wear Abercrombie a lot and show off to their friends, etc.