Surely because it is embarrassing to get the spelling wrong and his reaction shows that he at least is aware of that whatever the reason for it.

It made me smirk when for the second 'N' it was clearly a 'U' on its side, which he placed directly next to the first 'N' which was clearly an 'N'. I don't know how he couldn't tell that there was a difference between the 'N' and the 'U' on its side even though they were right next to each other.

They should keep doing it.
I don't mean to be cruel, but in the last series people on here were saying how they went lightly on some housemates. I think it's a good idea to capitalise on ALL housemates weaknesses and once they identify a weakness do it more.
Not bully them, but in a case like this when somebody's arrogance won't allow them to admit their own failings, keep doing things to them until they do.
For example, bring all the vain narcissists down to earth by forcing them to reassess themselves as people.

That's why Danny is breaking rocks in the hot sun for a living.....

Even with words which can be testing, the test wouldn't be so much whether they can spell or not, it's about their reaction.
If they hold their hands up and smile with embarrassment admitting their flaws, fair play to them. But when one of them like Danny throws his toys out of the pram because BB in his opinions played a trick on him, instead of admitting to his own failings, then they deserve to have a degree of pressure placed on them.

http://bigbrother.channel5.com/day-5...ome-alone-time

As I said Sarah wasn't going to let a bit of bad spelling get in the way of a showmance. Don't feel the need to apologise or anything

But he placed the blame at BB's feet for his own inability to spell.

I know. He was acting defensively and angrily and blaming BB is doing that. Don't people act defensively when they're embarrassed about something?