Can I reject a prospective tenant because they're annoying?

[Aliz Raksi]

I'm starting to receive applications for a unit I have for rent. As a full-time working single mom, I don't respond to texts, calls or emails right away and try to block out time once or twice a week to respond to everyone at once. Well, one Saturday morning, I woke up to 10 missed calls and multiple voicemails from one prospective applicant. After that, I didn't even want to call them back (I absolutely hate dealing with pushy people over the phone), so I simply texted them my standard reply, thank you for your interest, the virtual open house will be on XYZ date, etc. We exchange a few texts, all seems well. Then, 5 days later, I went to the property and his parents were waiting for me, they had showed up unannounced. It was super awkward because they didn't speak English, either, I had my current tenants and an inspector translate. I dread to think about how long must they have been doing the stakeout or disturbing the tenants, waiting for me. Gah! I emailed them the rental application but I feel that this is an overstepping of boundaries and I don't want to deal with tenants who are going to be like this. How would you word the rejection letter? I have not started screening tenants yet, and I have received applications before them, so who knows if they would even get to the phase of being accepted, but I was just also wondering about the legality of this and how would you word the rejection letter? In case it matters, this is in Los Angeles, CA.