I've seen several manly necklaces I like -- usually hemp cord macrame into a "chain" with a central, earthy-colored bead in the middle (or shell) and a knot-and-loop closure.
Have also seen ones I like that have a bead - charm - bead approach for the central bit. The charms I like are usually silver or pewter discs stamped with a sign (they look a bit like sealing wax embosses, actually).
Third thought: Take three leather strands, run a big bead down them (all three strands go through the bead), join in the back. The separation of the leather strands might look cool against a manly chest.
No glitz or bling, please, tho. Ugh.
I like the one Dex posted, too.
Then again, I'm not a man, so what do I know?
"You'd be surprised at how much it costs to look this cheap." -- Dolly Parton