David Letterman GRILLS Lindsay Lohan — Are You An Addict???

David Letterman grilled Lindsay Lohan like a cheeseburger today … firing off question after question about her upcoming stint in rehab … until Lindsay finally shot back with a dig of her own.

Letterman broke the ice by asking, “Aren”t you supposed to be in rehab now”

Lindsay responded, “Don”t you watch anything that goes on What are you a tabloid now”

Lohan eventually told Dave what he wanted to hear — she”ll be entering rehab on May 2 and believes it”s “a blessing and not a curse.”

Letterman kept pressing … asking if Lohan believes she truly has an addiction problem — and that”s when Lindsay hit back.