Like a few things, it seems just a little bizarre to me: You seem to be able to flag your own posts !? Is that logical ? Is there a use for this ?
And you can flag posts in PMs (your own also included), which may be a good thing, but the window popping up is the same as in public messages proposing for example “this is off-topic” … “…should be moved elsewhere”. It’s nothing really important, but it’s just a bit strange.
Sure, maybe you want a staff member to help with something related to your post.
You’re right. 
I just thought about this afterwards and was about to edit my post. You were too quick 
Ok, I will understand if “it’s good like it is”, but as I created the topic, I will put it out there:
A small possible improvement would be to maybe suppress 2 of the 4 options when you flag your own posts. It seems the option to PM the user is already suppressed when it’s one of your own post. This would follow the same rationale and I guess be done at the same place in the code (if own post, then remove this options): Remove “it’s inappropriate” and “it’s spam”. Who in their right mind would flag their post for that, rather than edit or delete it ? I guess you can probably imagine something, but the user can still write something in the “something else” box if needed. It would remove the just a little “bizarre” part where you have the possibility to flag your own posts for these reasons, which seems quite silly.
Another way to do it, which I quite like, would be to only have a box to say why the flag is done, similar to the one for “something else”: “Please describe why the staff should have a look at this post or what you would like them to do”, or something like that. People can still ask for a topic split this way (or maybe it’s better to keep a clickable option for that, I don’t know).
Remove “it’s off-topic” from inside PMs flags. Same, maybe it can have a use on occasion, but it feels a little weird and would be best removed, I feel. Something can still be asked in the “something else” box.
(Just a thought: What happens with the inside PMs flags when using the encrypt plugin ? Staff is supposed to be unable to read the posts then, isn’t it ? Feels a little off to be able to flag then, if it’s still possible. And it may make some people ask themselves questions. Why can you flag if you’re told it’s encrypted and unreadable ? That’s how some “conspiracy theories” probably start )