I am imagining a person who is involuntarily celibate or not yet sexually active thinking “Sex can be boring?  I don’t believe it!”

It can be and often is.  Any of the following reasons can be far more complicated than I write or can be combined with other reasons for any man or woman. I am just putting forth some situations in which sex can be boring for one or both people regardless of gender.

1. Your regular partner has a routine that rarely if ever varies: He stimulates Body Part A then Body Part B, then C, and so on. There are rarely any changes to his love making pattern and there are no surprises. And above all, his is not a sequence of events that you would choose.  Or, if your partner is female she requires a very specific touch to a very specific place and for a predictable length of time in order to orgasm.  Particularly if you have already come, this focused partner stimulation can be, well, boring. A possible solution:  Announce that this evening you are running the event and then do so with a different program.  Introduce a vibrator, maybe, so that stimulation can be more direct and not as lengthy. Maybe introduce something new you would like to try.  Change things up so that your partner can perhaps pick up some new ideas or relax and enjoy when you occasionally lead the dance.
2. You and your partner have been doing the same thing with each other for a very long time. You have decided on a series of moves that work for you both, or for at least one of you. If there are no surprises, if nothing changes – not the place, the time, the particular activities, and, of course, not the partner, even the best of happenings can get stale.  A possible solution: Choose a time when you are both available for an important conversation and make some suggestions:  “Would you like to have sex outdoors?” or “I would love to take a bath with you.  What do you think?” If your suggestions are vetoed you will have to just spring something new on your partner and hope that result is a happy surprise.
3. You are not getting your needs met. You haven’t asked your partner for, let’s say, anal play, or you have asked and your partner isn’t interested.  Oh yes, and you are in a monogamous relationship so you can’t go elsewhere for that particular activity. A possible solution: Rent a video or buy a book about your fantasy activity.  Ask your partner to read it or watch with you and then explain how important this thing, whatever it is, is to you and see what you can negotiate.
4. Your partner, whom you love dearly, is not your physical type. Your fantasies revolve around big these or small those, hairy where s/he is smooth, or a different body type altogether. Whom you love and what your fantasies are about just don’t match. Possible solution: if this is not something your partner can play, wearing a wig or shaving the pubic area for instance, you can watch videos that display your ideal while you masturbate.  If none of these suggestions scratch your itch you might consider asking your partner for a “hall pass” for a one time experience with your fantasy partner.
5. You are really not monogamous but you are in a monogamous relationship. Some people are just “adrenaline junkies”, who need variety in their lives, particularly sexual variety, that one partner just can’t fulfill. Or you love the chase rather than the culmination of it and there is no chase aspect in your  ongoing relationship. You’ve made your conquest and want more or other.  Potential solution:  If your partner can understand your nature and accept it, you can have a very good sex life.  Home base is often the most satisfying after an adventure.  However, you need your partner’s consent here and that’s often iffy to obtain.

Often any of these issues can be complicated and a source of great pain within a couple. The solutions I give here are quite simplistic when a couple needs to look at all the consequences of accepting or refusing outright my “solutions”.  When there is an absolute stalemate couples counseling can often be very helpful if only for Person A to finally “get it” and understand how important the issue is to Person B, presumably someone they love and want to be happy, to get his or her needs met.