Who written on the door

Salman Khan arrives home to find 'Salman is
an idiot' written right in front of his door.
He says to his friend: 'That 's strange - this
seems to be written in urine ... . Do some
tests and find out who did it.'
Later that day, his friend returns to Salman.
'Bad news, I' m afraid! The urine is that of
Vivek Oberoi!'
'I would have expected that. .. ', Salman says ,
'Why is that bad?'
'Well , the handwriting is Aishwarya 's!'