Eh, people, let's keep egos in check. Agree to disagree, please. Peace in the thread...

I don't think I would reject for no reason, but sometimes if I'm 'unsure', I will wait a few hours to reply. This also helps me find the impatient people. You know, those people who PM again in under 2 hours going; "You could have just said no!"

And I reply; "I am multitasking right now and was contemplating RPing with you, but you clearly are impatient and I don't feel we'll work well together."

Honestly, I give people 24 hours to reply to me if I message them first. If I do not get a reply, I assume they had no interest. If they message back later, yey, if not, again, I accept they didn't care. Sure, it is polite to say 'no thank you', but sometimes...like when people break rules in their first post to you by asking for things you don't want, it's hard to say 'no'. They often come back with "Why not?". Then you have to tell them and they get all mad that YOU don't like that THEY ignored the rules...

I remember when I had a group chat. Very big. I ran the screening like I ran the RP (very organized style due it being an organization, war, military style RP). They had to fill out bios. I would reject any female bios that focused more on talking about how 'hot' their character was instead of why they were in the organization to begin with. As the rules stated, it's a 'war' roleplay, not a beauty pageant. 
I'd also tell people I wouldn't accept it if the 'reason' they came to the organization wasn't a decent enough reason.
People who cared and REALLY wanted in would rewrite and understand. Those who were children, impatient, or just immature, would vanish or become brats and be mad at me.