Is it frivolous to be delighted by someone’s command over the English language? Yes, it is. Especially when it’s inappropriate (not to mention juvenile) as well.
But ah, a little touch of the ‘not-exactly-approved’ greases the wheels of a routine day. And hmm…who’s going to be able to tell the diffrence between a polite smile and an ‘I’m so charmed by you’ one? 😉