Ok to get this achievement start out by heading after Benny in the
Tops Casino at New Vegas.
When you get there be sure to talk to Swank the Receptionist, and he will reveal that he is friends with Benny.
After you pass a few speech checks he will allow you to carry guns into the casino (He will also give you Benny's suite key and stall him for you to go look around.)
Go to Benny's suite on the 13th floor and take anything you want. Then talk to Yes Man in Benny's suite to reveal Benny's plan for the Platinum Chip.
Once your done with the ages of talking to Yes Man, go downstairs and talk to Benny or Swank. There are many variables that can take place here. . .
1) You can talk to Benny and choose the positive/peaceful solution, he will grant you the key to the Presidential suite. Afterwords he sends 4 body guards to take care of you, while he flees to 'The Fort'
2) You can straight up murder Benny right there, but just about every employee will be attacking you. (If you do this option on the main floor, only his 4 body guards will attack you before its peaceful again.)
3) If you have the 'Black Widow' perk (Female Characters only) You can seduce Benny into taking you to his room and having sex with him. After this there will be an option to kill him (This does not alert any guards or give negative karma)
4) You could also talk to Swank instead, try and talk him into believing that Benny needs to be taken care of, Swank will then send Benny to his room so you may talk to or kill Benny. (This goes unnoticed and the casino will not go hostile if he is killed in this manner.)