A person who randomly sexts someone they don't even know. Thus, freaking them out. Or, someone who sexts so often that they sext the wrong person.
Sext Offender: Hey baby, I'm naked and thinking about you.
Recipient: Who is this?
Sext Offender: I bet you would like it if I came over there and took off your pants.
Sext Offender's Mother: Mike, this is your Mother.
Person 1: Why did Ashley dump Mike?
Person 2: Mike got caught sexting some girl.
Person 1: I bet he's a repeat sext offender.