Have you tired 'Fuck off, loser'

Or failing that, the thing that works for anyone being bullied:

'Strange how you're giving all this time and attention to someone you despise so much.'

or:

'Say what you like to me - at least while you're picking on me, you're not bothering anyone else, who might actually care what you think'

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"Time flies like an arrow -
Fruit flies like a banana"

M Y - N A U G H T Y - P I C T U R E S ! !