You can use WHERE NOT (columnName IN (things 'not in')
Like this example :
SELECT post_id, message
FROM stream
WHERE source_id IN ( SELECT page_id
FROM page
WHERE name='coca-cola'
)
AND NOT (message IN ( 'probando cocacola'
, 'Stijn '
, 'Ha ha ha me crezy hu'
, ''
)
)
LIMIT 50