My friends mother died and I wrote in the memoriam book "too bad, so sad" and now everybody's mad at me...why?

It's sarcasm.

That would be very rude to anyone. When people say that, it's usually a sarcastic phrase meaning that the situation doesn't really matter...What you should do now is give a sincere apology and don't forget to mention that you were just too dumb at that moment to realize that phrase was sarcastic and didn't sound right.

That phrase basically screams sarcasm. Like it showed that you didnt care that her mom died and it basically shows no respect. You say that when a person drops their food or something. That was the wrong thing to say. You need to apologize

First of all, you just said 'F#<k them' about a friend whos MOTHER just died. You are a terrible friend, they deserve way better than you. Oh, and too bad, too sad sounds uncaring, cold, and sarcastic that's why their mad.

Oh my gosh! Thats so sad that their mom died. Its definitely not a joke and they all think you are taking it like one try to be more polite. I wouldn't want to talk to you if you said that about my mom.

Other people write it when they are making fun of a loss.

It sounds sarcastic and sounds like you making fun of his loss :I