The 40th birthday is often treated as a milestone birthday. For men, especially, the birthday may symbolically signify the start of middle age, which is why many 40th birthday parties have an "over the hill" theme to them. The gift you give to the birthday boy may in part depend on his sense of humor. Give the man turning 40 in your life a gift that he will treasure or one that will make him laugh.
Many 40th birthday parties are roasts. They are meant to be funny, signifying the death of the birthday guy's youth. If this is the case and the guest of honor has a good sense of humor, consider giving him a gag gift. Wrap up a magazine printed in large print and geared toward seniors and tie a pair of reading glasses to the ribbon. Give him a bottle of "blue pills" (use blue candy) and set a cane or walker by his chair. Other gag gift ideas include other "old man" items, such as false teeth, flannel pajamas, or a can of Rogaine if the man is balding.
Recapture your man's feeling of youth by giving him the gift of adventure. Think of something he's always wanted to do and then arrange for it to happen. For example, if he's always wanted to go paragliding, pay for the lesson, pick him up in the car and don't give him a chance to back out of it. Other ideas could include a round of golf at an expensive and fancy resort, a night of gambling, or even a week-long adventure vacation if you can afford it, such as a trip to the jungles of Costa Rica for some river rafting and a ride or two on a zip line.
Most men don't outgrow their love of expensive toys. Get together with some friends and chip in for a 40th birthday gift he will truly treasure. Perhaps the man in your life has been eyeing his son's iPhone or his friend's brand-new laptop computer. Getting him something expensive and impractical that he would never purchase for himself is a great way to stave off that middle-age crisis---unless, of course, that lavish gift is a sport's car. In that case, prepare yourself for the crisis!
Give the man in your life the gift of words. Write a list of 40 things that you love about him and then read it aloud to him while dining on his favorite meal during a romantic evening out. Alternately, ask everyone in the family to write one complimentary thing about him. Once you have 40 sentences, give them to your man. It will be treasure he will remember for a long time.