Formally, a sociopath is someone who does or is characterized by 3 or more of the following:
- fails to conform to social norms, such as repeatedly performing acts that warrant an arrest
- deceitfulness, such as repeated lying, conning others for a good reason or not, and/or using aliases
- failure to plan ahead, or impulsivity
- aggressiveness or irritability
- disregard for safety of oneself and others
- consistent irresponsibility, such as inability to honor obligations
- lack of remorse, such as being indifferent to or rationalizing having hurt, mistreated, or stolen from another.

A good example of a sociopath is the part perfectly played by Angelina Jolie in the movie Girl, Interrupted.

By a more common definition, a sociopath is a manipulative somebody who cannot and does not want to feel love or affection, and simply uses others for his/her own benefit.

I've known people like that. It's very nice to tell them to fuck off.