Many crafters have trouble making masculine cards. I keep some special stamp sets for the men in my life and usually have little trouble making them cards for their birthdays. Want to know my secrets? I consider the interests of the fellows around me and get stamp sets to coincide with those - fishing, boating and camping seem to be themes around here. Some just like the ocean. If all else fails and I don't know their interests too well, I use stars or Fleur-de-lis instead of flowers, and use less of them. Or I select a nice strong tree as my main image. I use stronger colours like reds, browns, greens, blacks, yellows, oranges and blues, usually, but purples can be fine too. Whimsy is good for boys so I make little monsters or creatures. They also like robots, in some cases, but I have no robot stamp sets yet :) Lego is fun. And teens love to be sporty quite often so I choose action figures or something that can go fast, like cars, speedboats, etc. Hmm. Does that give you some ideas?
Here are a couple of masculine cards I made recently to add to the inspiration!
Let me know if you need a supply list for any of these cards. All images are current at time of publishing and can be found in my Stampin' Up! shop.