Where do you draw the line Hully?
Where?
If I posted a 'joke' thread about kids with special needs would that be ok?
Comedians like Frankie Boyle get away with it because they are making jokes to an audience specific target. Same with Jimmy Carr. But on Mumsnet you have people of all races, religions and walks of life. You have people who have been abused as children, parents whose children have special needs or cancer, people who are disabled, people who have suffered racist abuse, who have been racially attacked, who have gone through the heartache of their children with SN being bullied and attacked. Therefore there is a time and a place and Mumsnet is not one of them.
There is a misconception that everyone on Mumsnet is thick-skinned and we are a nest of vipers etc, but it's not true. Each of us have had our own experiences and hardships to deal with.
If this is about that 'Inglish' thread that it was a poorly thought-out thread. The OP said it was a bored fred and you don't have to be a regular Mumsnetter to know that such a thread will bring out the racists and cause a lot of upset. In my mind she was stirring because she was bored and wanted to watch a bunfight.
Don't berate people for showing some sensitivity. Race is a sensitive topic and unless you've been a victim of racism, unless you've been attacked and spat at then I guess you'll never know how much of a sensitive topic it is. If the OP wanted to discuss what she overheard, there were much better ways of doing it than the crass way she chose.