Ha ... ha ... ha ...
You don't know your audience
What makes something funny is a shared reality. Humor only works when the listener can relate to what you're saying. Joking about the pains of going to private school to someone who didn't have such a privileged upbringing, or about your favorite childhood TV show to someone who grew up in a foreign country will likely result in a joke that falls flat.
Your timing's off
It's a safe bet that there are certain times in life you should not attempt to tell a joke. At a funeral, while in the classroom, during a disaster or when someone's getting laid off are all scenarios where you should probably save your witty repartee. Much like understanding your audience, understanding the right time to tell a joke is pivotal to getting a laugh.
You're being mean
Are your jokes directed at someone's physical appearance, ethnicity, nationality, religion, economic status, religion, education or lifestyle? While you may think the jokes are perfectly funny, chances are others will find them hurtful, offensive and cruel. Avoid humor that demeans someone else, as it's not a joke, it's bullying.
You're inflexible
Have you ever told a joke that someone didn't understand, so you tried to explain it, but only grew more irritated as your listener still didn't get it? We hate to break it to you but that's not their fault, it's yours. Being inflexible while trying to make someone laugh is a sure-fire way to make your joke fall flat. Not everyone finds the same things funny, so lighten up and be willing to adjust in order to keep the good times rolling.
You're trying to be cool
People can spot a poser a mile away. When your humor is a front to try to look cool, it's going to be a major turn-off to your audience. Relax, stop trying to stand out and just let your humor flow naturally. People are more receptive when the person making them laugh is down-to-earth and real.
You're trying too hard
Much like those who try to look cool (or are inflexible), people who try too hard to be funny can come across as obnoxious. Slapstick humor, including strange voices and funny faces, can work for some people (like Jim Carrey) but for others, it comes across as forceful and inauthentic. Put the act aside and stop trying to push your jokes. If you're funny, it will happen without all the effort.
