All birthdays are special, but some are more special than others. For adults, these are the milestone birthdays; the ones that make you feel the passage of time. They arrive when it's time for the human body odometer to turn over to the next decade.
There are two ways to approach milestone parties - kindly or humorously. If you take the humorous approach, be sure your guest of honor has a sense of humor. The purpose of this party, like any birthday party, is to make your friend feel loved and cherished. You want to cheer him up and highlight the positive side of aging, e.g. all the friends he's managed to acquire over his lifetime. You don't want to depress your friend about hitting a milestone birthday with old age jokes and gags if he doesn't really have a funny bone. Proceed with caution and make sure the guests aren't laughing at the birthday boy's expense.
The Humorous Approach
The first adult milestone birthday strikes at age 30, when you're really much younger than you feel. By this milestone you may have gotten married, started a family and purchased your first home. And if you haven't done these things, you're probably feeling the pressure that you should. This is the age when friends begin to think it's funny to host an "over the hill" party for you. And it's the only birthday, I think where it really is funny to host that kind of party since 30 is hardly "over the hill!"
When you host an "over the hill" party, ask your guests to bring small gifts that will tease the guest of honor about how old he or she has become. For example, laxatives, reading glasses, hair dye, adult diapers and denture cream. Decorations usually include black balloons and streamers. Food might include anything soft, like baby food for your poor, toothless, geriatric friend.
Another variation on the "over the hill" party is the mock funeral party. Request that guests come dressed in clothes of mourning. Ask some of them to read a eulogy. Set an obituary at each place. You can even use it as a placecard. Decorate with lilies and play organ music during the party. Black is, once again, the color scheme for this celebration. Make a cake in the shape of a tombstone. This is easy to do by attaching a rectangular cake to a half of a round cake with a diameter that matches the width of the rectangle. Frost it in gray or white and write R.I.P. on it with black decorator icing. (One word of advice for this particular party - be sure that the birthday boy has not recently experienced any deaths of a close friend or family member. This party loses its humor if it hits too close to home.)