My parents on FB wouldn't embarrass me intentionally, and I'd have to live with that, in a grin-and-bear-it way
By the same token, one of my kids has a FB account but I'm not bothering him. He may not approve of what his old man does
For me it's mostly the pictures. There are so many photos of me on facebook in situations (read: drunk off my ass) that I'd simply rather my parents never see.