I actually kind of like smirk. I think it all comes down to how you employ it. My smirking characters are usually doing it to tease others.
I was guilty of this as a teen writing fanfics and have been doing my very best to eliminate all traces of it in my writing ever since.
Senpai basically refers to anyone with more experience in a certain domain that yourself. Be it your colleague who’s been at the office longer than yourself or an upperclassman in school/college. It’s not necessarily a term of endearment more like an honorific? You also wouldn’t call a master or teacher senpai.
I find purred very fitting to describe annoying and/or clingy characters.
As someone who’s nostrils flare when I get angry or flutter when I laugh, can’t say I find it very disturbing. I am a bit self-conscious about it so seeing it happen to others - even fictional characters - makes me feel a tiny bit better?