Over the years, Zak, Nick and Aaron have invited many guests to participate in some of their most memorable investigations. Motley Crue's Vince Neil, mixed martial arts fighter Brendan Schaub, actor Chad Lindberg and the Hollywood Ghost Hunters are just a few of the guests who got their hands dirty on a lockdown with the guys. After showing a complete lack of fear when faced with shocking evidence, these guests will go down in GAC history as some of the most courageous first timers ever.