When a man walks into a space where there are one or more men in a way that announces his alpha maleness in some obviously way. This can be with a slow, shoulder-swinging walk, or just with a tough guy look on his face or with another affected gesture of nonchalance.

It can be as little as shooting you with a look though to 'let you know he's there' and is the alpha male within this particular territory, unless you have any ambitions to prove otherwise