From the NHS website :
Avoid drinking grapefruit juice if you are taking simvastatin. Grapefruit juice reduces the breakdown by the liver of simvastatin, which raises the level of simvastatin in the blood and makes you more likely to get side effects.
Atorvastatin interacts with grapefruit juice if you drink large quantities, but an occasional glass is thought to be safe.
It is safe to drink grapefruit juice if you are taking any of the other statins.
It's only grapefruit - other citrus is OK.
dave