Nothing says masculine decor like a set of antlers, leather upholstery and over-sized British furniture/decor.
Here are my suggestions for a manly decor:
Accessories. Pillows and plaid throw via Pendleton, baroque weathered mirror via Restoration Hardware, horse head sculpture via Haus Interiors, Safety Deposit via Haus Interior, Vintage inspired scale via Restoration Hardware
Lighting. Flush mount ceiling fixture via Circa Lighting, exterior wall sconce via Interieurs, chain link cargo cluster pendant via Davey Lighting, '67 boom arm floor lamp via Ralph Lauren Home, Blackened bronze flush mount ceiling fixture via School House Electric, vase uplighter via Soane
Furniture. Trunk side table via ABC Home, tufted sofa via Ralph Lauren Home, metal armoire via Interieurs, Chinese inspired rattan cocktail table via Ralph Lauren Home, vinyl poof and leather desk chair via 1stdibs, bascule desk via Soane