I’m afraid this is not really a very good question for the StackExchange format, because it does not lead to a clear, best answer. For example, just because I might think that a
gentle reminder sounds less like you’re leaning on someone than a
friendly reminder might, others might have just the opposite reaction, and there is no way to judge one above the other. This is also extremely culturally-biased, so what is considered eminently polite and non-threatening in say New Jersey might seem like brutal enforcement by a crime syndicate in say Japan. :) —
tchrist 2 mins ago