That's fine, but ending on a disrespectful tone is generally a bad idea.

I don't see the above quote as particularly disrespectful in context. It's a bit like a friend who has just spent half an hour talking you into going for that new wonderful job, and says 'or you could stay in your crummy current job'.

Basically he's saying: "I think this way of doing things is awesome. Here's how to do it my way. Your way of doing it is crappy compared to mine, but hey it's your choice to continue being a substandard performer."

Even your example is riddled with condescension, with your judgment from on high that your friend's job is "crummy". It's not only disrespectful; it betrays an unsavory vanity on your part.