Anonymous“whatever rock he had been hiding under.”
To "hide under a rock" can mean a couple of things, depending on the context. The non-judgmental meaning is someone who is isolated and uninvolved in the daily world. The judgmental meaning is to compare someone to the critters you will find if you look under a rock (not a very appealing image). I don't know the context of the sentence you are quoting so you will have to decide which meaning applies.
Anonymous “Mandy didn't know how it felt to love someone and have it ripped away from you.”
Presumably April had a love affair end badly and Mandy is being insensitive in her reaction. Thus April is lashing out by pointing out that Mandy could not possibly understand since she has never been in a similar situation. That is, never had someone she loves taken from her (ripped away).
Anonymous “Mandy said she didn't want to kill April, because the police did man hunts for murderers.”
The word is "manhunt"
an organized search (by police) for a person (charged with a crime)