You can read the whole rejection letter here.
Basically, NBC wants PETA to remove images like a woman "screwing
herself with broccoli" and "asparagus on her lap appearing as if it is
ready to be inserted into vagina." That's not asking too much, really.
What NBC honestly missed are the two most egregious offenses committed
by the ad: The first being that PETA submits no information with which
to back up its dubious claim that vegetarians have better sex. The
other? Well, the ad is just plain stupid. When did PETA get the
idea that best way to get people to stop exploiting animals is to
exploit women instead? Like some Buffalo wing-scarfing, Bud-swilling
neophyte is going to see this commercial, toss his plate on the ground
in excitement and exclaim, "Ya'll know wut? I'z gonna stop eating them
thar chicken wangs because, doggonit, I deserve to fulfill mah Earthlee
dee-sires as much as them Sex in the City gals do!" No. No,
that's never going to happen. Instead PETA is going to get made fun of
ad nauseum by everyone -- vegetarians included. Meanwhile, the
brainchildren that run that sinking ship will perceive the incoming
hits as a success, and in turn produce an ad featuring Mickey Rourke going down on a plate of mashed potatoes. Sends chills up your spine.