I wouldnt listen to them man....
Anything can be learned and Developed!!! Anything....
Start excercising your brain powers man. Excell your train of thought into uncharted territories. Start learning new stuff everyday, work on logical problems, like a math book or something, get your brain quick and calculating easily.
If you are worried that you are lacking in wit, Then I assume your brain is dole.
Aside from getting you're brain faster I think the most important key to wit, or humor i should say is a 'CREATIVE IMAGINATION' ... If you have a creative imagination then you by no means will be dole.
Then just ground yourself, meaning be a down-to-earth human. Someone who understands other humans, that way you wont be saying out of place things that make you look like a weird fvcker half the time (being weird is okay, if your are purposely doing it to be funny... being just plain weird is.. well its weird).
Confidence and being fresh and down to earth will present the type of sense of humor people will enjoy.
Aside from that Be creative!!!!
Trust me you can develop any physical or mental ability you want to. Nothing is impossible... you werent unlucky. In fact you have done something we all should be doing, you have identified one of your weaknesses and now you will be turning it into a strength. :yes:
... But make sure not to "try" too hard to be funny. Only say or do the things that you think are funny. When you are by yourself start people watching, or observing things.. Becoming more aware of your surroundings will help for material. And laugh at the things you observe, wake that sleeping sense of humor of yours.
Dont laugh at people in a cruel way (passing judgment and being negative 24/7 is not funny... well, just use it sparringly atleast =P). But laugh at people in a lighthearted way, enjoy people. Enjoy life. Find it funny and easy going.. And play with your imagination. Be creative.. have fun man.. Just start playing like that and sure enough your wit will be growing by the day...
Eventually if you keep building on it and strengthening it you will have such a witty brain woman will be clawing to soak you in. You will give them and everyone around you that playful creative release we all want, but usually forget about as adults... Good Luck!