1. The person in the audience at a concert, play, movie, etc, who forgot to turn off his/her cell phone and is reminded of that fact by getting a call during the event, much to the irritation of everyone else nearby.
2. Someone who feels the need to yell into his/her cell phone far above and beyond normal conversational volume, much to the irritation of everyone else nearby.
Distant reverberating phone ring: beep boop boop beepity beep boop boop!
Other people in audience: What a celltard!
Celltard: BLAH BLAH BLLAAHHHH! BBBLLLAAHHH!
Other people: Shh!