Claiming Bulletproof is like claiming Serial Killer.
If you claim Vig you can at least get a few people to try and use you like a tool (in a normal game).
I'm pretty sure she was referring to what power she'd take had she rolled SK. SK's this game could choose one of BP, Investigative Immune and Juggernaut powers.
But yeah bulletproof as a fakeclaim generally sucks, and I haven't even rolled scum yet.
