I am a bisexual and I use it for specific, definitive reasons.
I interact differently with penises and vaginas and what is standard in connection with them in cultural, social, sexual and bio-terms.

I'm not a pan, omni, or *-sexual, all of which in most statements I've heard or read comes across as "man, lookit how open I am!"

You may not like my use, but I've found the insistence that I see it in a particular not-my-wiring way to be offensive to the extreme, since I operate under the faulty assumption that people can choose their own labels as long as they don't implant them in others. I like pretty, and I like certain kinds of pretty, just like everyone, everyone else. If past actions and statements between us still makes you feel excluded by me, then I consider all of them failures.

This is not meant to be angry or aggressive, but it is a statement on my own position.