This should be easier to answer than the worst drama serial question.... Cos unlike bad drama shows, which will finally come to an end, bad acting from the same actor will continue to haunt us for a long time.
Personally i think Julian Hee... he's the worst actor since Robin Leong and Benedict Goh. He has the same expression for everything. Kinda like Terence Cao.
Girls-wise, I have to say Joanne Peh. I know she's the IT-girl, she's book-smart and all that, but really if you notice her acting....cannot make it lah...
There was this NKF show where Julian Hee and Joanne Peh acted as lovers and they were breaking up in a scene. That scene was the best example of the worst acting i saw in recent years.