By creating a costume that is a play-on-words, you are sure to get many laughs and even more inquiries into the meaning of your costume. Not only will a play-on-words costume get a lot of laughs, but they are simple to make, often with many common household items or a quick trip to the hobby store.
Opening up a Can of Worms
Make trouble by "opening up a can of worms." Cut out the bottom of a round (and clean) trash can, spray paint it silver and paint the word "worms" on the front. The worms can be made by purchasing several pair of pantyhose, cutting off the legs and stuffing each leg with newspaper or fabric filler. By taping the worms to the inside of the trash can and hanging them over the sides, the worms will look like they are crawling out. Carry the the trash can around all night by gluing a pair of suspenders to the inside of the can.
You can literally be a smarty pants by gluing tubes of Smarty Pants candies all over a pair of jeans, sweatpants or any type of pants you are willing to sacrifice (tape could also be used to save the integrity of the pants). Complete the costume by wearing a pair of thick-frame glasses in order to emphasize the "Smarty Pants" appearance.
This is not a 'serial' killer costume, but a 'cereal' killer, not only a play on words but much more light-hearted than dressing up as a notorious murderer. Being a cereal killer is incredibly easy. By simply purchasing a couple dozen boxes of individual serving size cereal boxes or several large boxes and gluing or taping the boxes to one's shirt and pants, topped off with the purchase of a fake plastic knife or creating one out of cardboard and foil, the 'cereal' killer costume is complete. This is the perfect costume for a cereal-lover.
God's Gift to Women
Women and men alike will find a "God's Gift to Women" costume amusing and sarcastic. This costume can be made by finding a cardboard box that is approximately the same length as the wearer's torso, then cutting holes for arms, legs and head. Wrap the box in wrapping paper, cutting out holes for the limbs. Decorate the box as desired, but be sure to include a large gift tag that says "To: Women, From: God." For extra detail, tie or tape a large bow to the top of the head.