Ever since i've grown up in thailand i've been sitting in a w shape with my legs. i've never had knee prob. but i've been told it's bad. is it really?

Probably ok: If you have been doing that for a long time and have no problems with it, it is probably ok. The most common reason some people might feel better sitting like that is a condition known as femoral anteversion. This is a rotational variation in the hip and patients often feel better with their hips internally rotated, thus the "w"position. Should not cause long term problems.