Not Plausible
OK now that I've got you in here...
So I may be hopelessly clueless about this but isn't there some kind of unwritten guy code? Something along the lines of don't pursue her as I'm into her. In the movie Alan asks and David says no not interested.
If Alan was Davids friend and David knew Alan was destructive towards women shouldn't David have said leave her alone. Or shouldn't David have asked Alan for help. "I'm stuck in the friend zone. She seems to like you and the crazy, could you teach me something to impress her?"
In real life people do stupid things all the time. The level of deviousness David showed though I would have thought he'd have tried something far less convoluted and more likely to succeed.
Your thoughts?