An unfriendly reminder

This is a friendly reminder to show, don't tell.

In fact, let's start with 'friendly reminder', as in 'this is a friendly reminder that your payment is overdue'. By using the adjective 'friendly' we're giving an impression that an unfriendly reminder is just around the corner, perhaps in the form of a bunch of guys who'll hold you down and piss up your nostrils until you pay up.

I couldn't function without a reminder notification on my calendar. Five minutes until a meeting, BING! Perfect. Being reminded is normal and I'd go so far as to say that these days people expect to be reminded to do most things. It's what the little robots in our pocket are for. A reminder just means, 'That thing you said you'd do a while back? Do it now.'

The people who write these friendly reminder emails could, instead, simply say, 'Hi there. We've noticed your account is overdue. Would you mind attending to that for us?'

This is a reminder that's friendly.