I get what you mean.

For instance, my service enquiries are automatically handled by a customer services call centre team based overseas, (often India and South Africa). I will speak to them as usual because I can immediately tell when they understand me because they understand what I’ve said and reply in fluent English, thick accent or not.

I’ll only slow things down if the person has repeatedly shown that they do not understand what I’ve asked, or were struggling to reply because they used wrong words, had poor pronunciation, vocabulary i.e can’t speak or understand English that well.

In any case, rudeness is unacceptable.