I'm not sure what to do. These guys want me to jam and rehearse with them, but I'm not sure I'm feeling it, but I don't want to back out the night before because I'm so sick and tired of people doing that to me.

But I'm just not feeling the music, so I'm not sure what to do.

I guess I feel like I'm fed up with waiting on people and them being unprepared and non-committal and now I feel like I'm going to be that person, but I'm just not digging the music. It's okay, but it's just...whatever, haha
And we will weave in and out of sanity unnoticed
Swirling in blissfully restless visions of all our bleary progress
Glowing in radiant madness
If you're not feeling it, you're not feeling it. Period. It'd be better to back out now, than to go and just not be into it. I think they'd respect you more for backing out now, than going and doing a bad job. Dig?
Take the worst of both worlds.

First, you have to completely change what style of music you like by listening to their style of music exclusively (even during sleep). Learn a whole bunch of songs in that style, then claim to know only songs in that style after forgetting all other songs in all other styles. Completely change your clothing style, outlook on life, and even speech patterns to suit the new style of music.

Second is the hard part. You have to kidnap these people, and lock them in a secure facility that only you know of. They must be kept separate for this to work. Attach headphones to them after securing them in chairs in empty rooms. Let them hear only your original style of music for a few months, feeding them and attending to their other needs only after they list their favorite aspects of whatever songs they just heard. They must be genuine, or else punish them. Normally, the volume should be at a pretty reasonable level to make sure that they don't hate it. The goal is to get them to associate good things with your original style of music.

After this, realize that you guys are still not compatible musically after having switched styles. Then move to a rural commune in far eastern Russia and try to make a living there by selling home-made bagels.

Or just try it out and see how it goes, and if it doesn't work, tell them so. Maybe you can reach a compromise, or maybe you'll just part ways.
"I agree with Matthew about everything" - Everyone