from Wiki "The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle."
Q:If each is the other's antiparticle then which is retrograde in time according to Feynman-Stueckelberg interpretation (FSI)? I mean if by the FSI antiparticles move backwards in time, and if $W^+$ and $W^-$ are each others antiparticle - then which one moves backwards in time?
EDIT: after noting David's and Ron's points I've added a diagram to illustrate the problem.
Suppose out of the vacuum $W^+$ and $W^-$ are created which then decay to electrons and neutrinos
It only makes sense if one of the W bosons is retrograde. I have arbitrarily placed the tilt of the W bosons, so they can be interchanged without loss of generality.