The only requirement for this custom design: masculine. Since I'm a pretty minimalist designer and I have a deep love for the color grey, it was pretty easy for me to keep it on the manly side. Using black, grey and bold typography, I had fun conveying the surprise aspect and the fact that he's turning 30 (not just your average birthday - I know because my next one will be 30 - yikes!). I printed the 'Shhh, it's a surprise' seal on the envelopes as well, and those were a hit.
AND - I hear he was indeed surprised. A success!