You cant undo the things you’ve said ; words once spoken cannot be erased, unless in rare instances the person has some sort of memory problem then you can have your fun with that I guess, normally though once you have said something that’s it, prepare for war.
It means therefore that
 we need to be careful about the things we say to people who we claim to care about.  We need to be more mindful of the words that ‘slip out’.  I find as I grow older I am becoming better at this, I know I have said a few things to people I wish I didn’t, not saying I am cured …getting better, not cured.
There are moments that we say things and as soon as the last syllable is pronouced a voice in our head goes – “oh boy you’ve really done it this time”.  You have limited choices at this point you could (1) pretend you didn’t say it, continue the conversation and just leave the person baffled (2) apologize (3) make it into a joke.  My advise  is to apologize even if you don’t mean it try to make them believe that you mean it and in the future be wary of the fact that you have the potential to say dumb things .
What is joke for school picney is death for crapaud! It might not seem a big deal to you but we have to always remember that we don’t have the right to determine how people react to the things we say or do and although it is true that some people over react, it is also true that there are basic rules that guide conversations and social relationships (read up on this it wouldn’t hurt infact it would help).