Earlier today, someone I know posed a question, one that is probably asked by more people than they think.
"What gives me the right to say I am _________?" (Insert gay, genderqueer, bisexual, pansexual, transgender, and so on here.)
A very complicated question, but one with a very simple sounding answer.
If you are _____, then you have the right to say you are. If you feel you fall under these labels, and you feel comfortable in using them, then for goodness sake, use them. There is nothing whatsoever wrong in doing so.
It's not as simple an answer as it seems, of course. In order to get to this answer, you have to overcome things. Your own reluctance. Your fear of what family, friends, and loved ones may say. Perhaps even the fact that what you call yourself today is vastly different from what you'd have called yourself just yesterday, or last week.
That last one is a very interesting one, because all through our lives, we are learning new things about ourselves, and about how we respond in regards to others. What we think of ourselves today, may not hold true tomorrow, or next week. That doesn't, however, make the labels we give ourselves today any less true. They are as true as the information we have about ourselves is.
Yesterday, someone may have felt the label bisexual covered them, and then today, they may get new information that makes them decide that they fall better under the pansexual or panromantic label. That doesn't make yesterday's label any less true, because at the time, they were.
The exception to this, of course, is if you genuinely don't fit the label, and you know it, but this misnomer usually occurs when other people label you, rather than when you label yourself.