This is a problem I'm commonly asked to help with at school.

Being in a high school there is the less mature students who find it fun to terrorise word users.

They use the word AutoCorrect feature, to change things like a full stop into 'you are a stupid w***e' and the letter n into 'you like a**l s*x' (without the asterisks)

if this happens to you, go to Tools -> AutoCorrect settings, and search down to 'n' or '.' and delete the entry.