some animals with frills (or something like it) use them to look bigger and impress other rivals of the same species or impress females (in that case normaly only males have frills and stuff like that) the Dilophosaurus would have absolutely no use for poison. It was the biggest predator of it's time, it had no reason to make itself look bigger because only an other Dilophosaurus would be a match for it. it was strong and probably also fast (btw it probably mostly ate prosauropods, and they moved slow). and like Mecheon said, a frill like that would need support, like bones or muscles, evidence of a frill has never been found, so there is absolutely NO reason to assume the the Dilophosaurus had a frill on it's neck. It's just as absurd to suggest that a Velociraptor had a frill.. so I have come to the conclusion that the frill on the Dilophosaurus is 100% FICTION. as for the poison spit, same with frill no reason to assume that the Dilophosaurus spat venom, so both are 100% FICTION.
Ofcourse it CAN be true (however unlikely) but we just haven't got ANYTHING to base it on.