Jennifer Aniston recently took part in a celebrity endorsement ad for UK's Sky Broadband. She not only looks stupid, but makes the brand look stupid as well. But we can't blame the whole thing on Aniston, since she's not the idiot who wrote the "script," for the commercial.
Jennifer Aniston Looks Stupid (4 photo + 2 video)
Here's another commercial endorsed by Jen. This one is more about "sex sells," than it is about the water.