I dunno, can't you just say "Dude, if you put me on the PIP, I'll have trouble leaving. Since what you're proposing amounts to disciplinary measures, I'll be quitting anyway; so why make it harder for me to get a new job?"
The dismissal process for underperformance here (UK) requires the employer to give warnings: one verbal, and two written, I think. The employer is also expected to help the employee meet the performance target. The PIP sounds like a checklist version of that help - it's not meant to help the employee, it's meant to hustle along the dismissal process. I'd take a job flipping burgers, rather than work for a boss that put me on a PIP.
