Dr Zuckerman (first name unknown) is a group therapist assigned to rehabilitate sex offenders. Stabler meets him while watching out for serial rapist Ray Schenkel to reoffend. As part of the con, Stabler would chortle with Schenkel about seeing Dr. Zuckerman as a crock, which Stabler actually figured regarding psych specialist.
Zuckerman actually particularly had Stabler face he might have problems with himself to not believe in recovery, nor be a threat to society. Zuckerman's approach was directly confronting the offenders for the sake of leaving them in a compromising, obligatory position to feel like they have no better choice but to confront their actions. Stabler pretended to have a good laugh about this with Schenkel as part of the rapport for the ruse.
Schenkel was eventually caught in the act and arrested. (SVU: "Demons")