The Doctor was obsessed with Clara and it was the Doctor’s unhealthy obsession with Clara that made him+Clara the Hybrid. [sort of like tumblr daddies who start Skyping and find themselves in prison or killing her parents or something after going too far as their relationship gets way too weird]
In short, the relationship itself was the hybrid. A little overkill? Maybe, but the Doctor’s weird obsession with Clara was going to end up weird and awkward regardless.
Or in short. The Hybrid = Toxic Relationship.
I’d rather it have been a toxic relationship between Dalek and Timelord but whatever…. although wait.. it was wasn’t it? shit moffat.