Worst things to say in prison

Prisoner #1: They call me ‘The Grim Keeper’ because I killed 36 people and kept their heads in my freezer.
Prisoner #2: They call me ‘Spike Tyson’ because I stabbed two cops through the heart with a piece of rebar as I was being arrested.
Prisoner #3: They call me ‘Snitchy McTattletale’ because I... uh... *sweats nervously*

"I'm a child molester." That will get you killed within days (rightfully so)