Bradley didn't duck Khan, he avoided the fight because he was in between promoters and didn't want to continue doing business with Gary Shaw. History has proven this to be the correct decision.
Alexander didn't duck Khan at 140, there was talk of them fighting but the talk largely went away after the string of Kotelnik, Bradley and Matthysse performances that left Alexander looking less than stellar. If anything Amir Khan is ducking Devon Alexander at 147.
I put my vote in for Vitali "ducking" Haye but I would say that is pretty arguable too, Haye was embarrassing against Wladimir and Vitali is quasi-retired by now so it's hard to call that straight ducking.