Bad words in my head

Sometimes, when I get frustwated, I say bad words in my head so that no one can hear me say em'.  (Mom starts to worry) 'What kind of bad words do you say in your head?'  Well, don't tell Dad okay?  Like sometimes I say hate and I know thats not nice and sometimes I say stupid, like 'that was so stupid!'  No one even hears me say it in my head!