|Date||May. 5th 2010|
Cemetery is the 736th xkcd comic.
The joke here is that the character is on the phone with someone using a hands-free headset, which looks like one of these (they were in style at the time)
The people around him don't know this, and think he is arguing with the people buried beneath him, since he is in a cemetery after all.
"Three headstones down, I got a call from my mom and it went from bad to worse."