My husband was turning 40 and recently became involved in motorcyles.  All of his friends also became involved in motorcyles (wives included). So my idea for his surprise 40th birthday was to throw him a biker birthday party.  The invitations were titled (his name) Birthday Biker Rally. I put some fun clipart of motorcyles and tattoos and such on the invitation.  On the invitation I stated that guests are to come in their best biker apparel. I also included tatoos in each invitation, enough for each party goer.  The yard was decorated in orange and black with a few signs announcing that he was 40. At the party we had a roast pig (hog) which we decorated with sunglasses and such to make it look like a biker hog.  My friends decided to distract my husband by taking him on a (men only) bike trip so this way when he showed up for the party he would arrive on his bike.  There was about 5 men taking the trip. They all arrived with their bikes with my husband leading the way. As my husband turned the corner of his house, he knew something was going on because there were large banners (made from sheets) announcing the biker rally hanging from the house. As he arrived, I had the DJ play "Bad to the Bone". It was very cool!  Most of the guests came dressed as "bikers".  Some of the guests really got into it too.  They had just as much fun getting ready as at the party. The cake was decorated in Harley Davidson colors (orange & black) with a plastic motorcyle on top of the cake.  My friends even got clever when giving gifts.  One of the gifts he received was training wheels for a bike.  I thought that was pretty clever. Many of the guests stated how much fun the party was and that they wanted me to plan their 40th birthday party.