1
You say 'I joke' instead of 'only joking' because you're too lazy to finish your sentence and you're too stupid to know the difference.
'I joke,' he said as he walked out of the classroom with a laptop full of cat videos.
'I joke,' she whispered as she sneaked a snack into her pants.
'I joke,' he said while typing 'download hentai free' into the school computer.