I often go for nature, outdoorsy or grape images (several of the menfolk I make for share an interest in wine) when I make masculine cards. I seem to err on the side of clean and simple - this may be partly because if my husband makes a spontaneous comment on any of my creations, it tends to be the CAS ones so I think of that as something that appeals to the male psyche!
I've attached a few so you've got something to look at! The first two are Cornish Heritage Farms stamps and are not ones the new owners have re-released so those would be harder to track down. The grapes are a retired SU! set (Gorgeous Grapvine), the birds are Crafty Secrets and the seahorse and fish are Darkroom Door.