Halogens F,Cl,Br,I...

Pardon me if its discussed before. Iodine is the heaviest halogen (good one) and Fluorine is the lightest one ( evil one?). Everywhere I read, it says,

F can displace Cl,Br,I.

Cl will displace Br and I,  but not F

Br will displace I, but not F and Cl.

So can Iodine not displace anything? Just get displace by lighter halogens....

I know some ppl think otherwise. HOW do u think, Iodine can displace lighter halogens.

thanks