This really seems to hit the nail on the head. And dear dog, he is just so passive. Liam just goes with whatever way the wind is blowing.
Imagine his thought process, if you will. "Dad wants me to partake of the side piece he's been lusting after...okay." Never mind that in some sick, twisted way Bill is trying to vicariously nail Steffy with Liam's stick of sorrow. Bill gave Liam a nudge and like a stone poised at the top of a long, steep hill, Liam just rolls with it. If one girl gives back a ring, then the obvious equal and opposite reaction is for that ring to boomerang onto the finger of the nearest warm female body. No wonder some ladies love Liam; he can be made to do anything they want.
And, man, I just can't see him as having the killer instinct to work for his father's business unless there's an opening in the mail room.