Horny camp counselors awaiting the arrival of their campers begin being picked off by a mysterious killer.

You definitely need to decide who the protagonist of this story is and what their goal is. What makes the killer so mysterious? What is the inciting incident of the story - what is the event that gets the story going?

This logline is pretty good start. Sounds like a cool 70's horror setup. You might want to think about using one hero instead of a group and describing their goal, even if it is just to survive. The irony may need a bit of work too. Id like to see an adjective pointing to loose morals. "Horny" is more of a way of thinking than an action. " promiscuous"? Is the killer from the heros past? How can you tie it together more as a story.