Purchase or select the appropriate attire for a Blue Man costume. Their shirts are loose and comfortable, with high necks and zippered backs. Their pants are also loose and sporty. Karate pants would work well.
Glue a washer on the shirt, in the middle of the chest (optional). This will look like the eyelets the Blue Men have on their shirts. In their show, they shoot liquid through their shirts through these holes.
Put on black boots, and tuck the bottom of your pants into these boots.
Shave your head completely bald or completely cover your hair with a blue swim cap.
Completely paint all exposed areas of your skin, including your face, the back and top of your head, ears, neck and hands. The Blue Man Group uses grease paint, since it never dries, allowing it to keep a glossy appearance throughout their show. Since grease paint is messy, you may prefer blue face paint.
Carry around drumsticks or tympani mallets to complete the look. The group members often use these props in their shows.