The thing is, humans are using your app. And when humans are facing something for the first time, if it's not friendly to them, they're going to be taken aback

The thing is, humans are using your app. And when humans are facing something for the first time, if it's not friendly to them, they're going to be taken aback and pissed off. Good products have friendly, warm, inviting copy. You could spin it around by turning it to 11, and call it something like "Speedsums for assholes". Then you could insult the user at every opportunity you get, using over the top curses in a tongue in cheek manner ("4 seconds to solve that? My guinea pig did better!"). If it's clear that it's meant in a satirical way, it'd be less shocking. However, this is much harder to pull off in a way that is funny and stays funny over time. So either make a product with clean, friendly copy - or make one that does the "evil coach" to the maximum. But certainly don't do a mix of the two- that's just very confusing emotionally. (recommended related reading: http://www.abookapart.com/products/designing-for-emotion http://www.abookapart.com/products/designing-for-emotion)