Why don't others laugh at my jokes?

I've made a couple jokes/pranks recently and hardly anyone laughs. I don't get it. They're suppose to be funny.

For instance I told a co-worker that not to put too much gel on his hair otherwise he'll look like a porcupine, get it porcupine. Only one laughed but no one else. Another time, I got my boyfriend by pranking him about being pregnant till I said ''gotcha, just kidding, lol''. The last one was about getting robbed and no one laughed. There is many others I've told during conversations but very few laugh.

I'm just trying to be funny. Can't anyone take a joke? Why don't others laugh at my jokes?

Why don't others laugh at my jokes?
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