Determine who the main character of your film is and what it is they want or what their goal is. Then figure out who or what is in their way stopping or preventing them from reaching their goal.
Think about what makes this ironic. All good log lines (especially true for comedies) are ironic. The irony is what makes it interesting and intriguing.
Write one sentence for each of the following; who, what (the goal), why (why they want the "what"), how (what is stopping them). Each of these four sentences should be descriptive.
Combine elements of all four sentences into two sentences that tell a complete story. This is your rough logline. Read it several times. Cut out any unnecessary words.
Read your log line to a few friends. Ask them to reiterate back to you what the movie is about. If they get the gist of it you're on the right track.
Wait a few days and then go back to it. Read it and see if it still makes sense. If needed, revise until it makes sense. Good luck!