People who say 'that' instead of 'who' when referring to someone, or instead of 'which' when adding information to a statement instead of adding a limitation.
In fact people who says 'that' when it's completely unnecessary in a sentence. For example, just taken from Stuff.co.nz
"....after she became concerned at her son's behaviour and reported that there was a gun in the house"
should read
"....after she became concerned at her son's behaviour and reported there was a gun in the house"
That really annoys me ;)

