I can't delete this

Tiff: I can't delete this. 

Me: Press the delete icon. 

(Tiff bangs on the keyboard) 

Tiff: It doesn't work. 

Me: What are you doing? 

Tiff: Pressing 'delete'. (Bangs some more) 

Me: The 'delete' icon, not the 'delete' key. The 'delete' key only works when you're using a word processing program. 

Tiff: Well, how am I supposed to know that?