The third most difficult part with humor is when you have to explain it.
The second most difficult is when someone actually gets offended.
The most difficult part is when a joke might cost you your career because you posted it on Facebook.
That is the prospect facing 33-year-old Melissa Cairns, a teacher in an Ohio middle school. Cairns' heinousness stems from an episode in her classroom at the Buchtel Community Learning Center.
"I made a bad mistake of thinking it was funny," she told ABC affiliate WEWS-TV.
What did she do? Well, a student had a problem with her binder (no, it wasn't full of women) and Cairns gave her some duct tape to fix it.
Instead, the student put the duct tape over her mouth. Kids being kids, several more decided to copy this amusement.
The kids allegedly asked Cairns to take a picture. Kids understand pictures better than words.
This being the modern world, Cairns didn't merely take the picture, she posted it onto her private Facebook page.
She captioned it: "Finally found a way to get them to be quiet!!!"
But we know that private Facebook pages are only relatively private. And you can never actually trust your Facebook friends, as these might largely be known as "people who aren't really your friends."
Sure enough, a fellow employee of the school reported her. She was ordered to take the picture down. This, she did.
Now, however, the school has suspended her, with a view to getting her fired.
"Students are protected under federal law and they have certain protections," Akron Board of Education President Jason Haas told WEWS-TV.
He added: "Has she violated the students' privacy? That's what we're concerned about. Everyone seems to be focused on the duct tape."
Perhaps some people should be focused on the excessive reaction to the picture.
Cairns told WEWS-TV: "Do I think that this one mistake should cost me the last 10 years of all the good I've done? Absolutely not. When your emotions are involved, that's when you learn things."
She meant that when the whole class is laughing, it's a great learning experience.
She is currently on unpaid leave. When she has her hearing in February, one question that the wise school board members might ask themselves is: "Who was harmed by this picture and its posting on Facebook?"
Cairns isn't the first teacher to be scolded by busier bodies because she expressed herself in social media.
Two years ago, Natalie Munroe, a Pennsylvania teacher, wrote on her blog about several of her students. One, for example, she characterized as a "whiny, simpering grade-grubber with an unrealistically high perception of own ability level."
Munroe was fired, but her pronouncements were entirely public. Cairns', at least theoretically, were not.
Teaching is a stressful business. Kids are not exactly an entertainment all the time. Who could forget the six girls in Nevada who used Facebook to organize an "Attack a Teacher Day?"
Would it really be fair to ruin a teacher's career because she posted a picture of a group of kids being kids on Facebook?