Start a new scene and go into wire frame mode. Add a plane and scale it up 5 units.
Building the man
Go into front view and select the cube and scale it down .5 units move it up .5 units (z axis) . Duplicate the cube and scale it down to .1 and move it to the side using ctrl so it is locked to the grid (we will use this later). Select our cube and press N to bring up the Transform Properties window and rename it to Right_Foot. Now go to the logic panel (F4) and change it from static to rigid body, set the radius to .6, and bounds to box. Now duplicate Right_Foot and move it over 1.2 units (x axis). Select both cubes, duplicate them, and move them up 1.2 units (z axis). Add a cube and scale it 1.1 units (x axis) and 1.2 units (z axis) and move it .6 units (x axis) and 3.6 units (z axis). In the logic panel, make it rigid body, radius of 1.2 and box bounds. Now duplicate one of the leg cubes (doesn't matter which one) and move it to [-1.2, 0, 4.3] (these are x, y, z world coordinates, you can enter these numbers in the Transform Properties window). Duplicate it again and move it to [-2.4, 0, 4.3], then select both arm pieces, duplicate them, and move them over 4.8 units (x axis). Duplicate one more cube and move it to [.6, 0 , 5.5]. Rename the cubes like in the picture.
Select the tiny cube we made in part 1. Go to the logic panel and make it rigid body, .1 radius, and sphere bounds. Using ctrl for grid lock, duplicate and move the cube to these positions. Give them sensible names like Right_Knee, Hip, Shoulder, etc. Select the right knee joint and go to the object panel (F7) and click Add Constraint->Rigid Body Joint. Do this twice. In the first constraint, change the field 'toObject' to Right_Leg and in the second to Right_Foot. Do this for the left knee. Select one of the hip joints, add two rigid body joint constraints, making the first one Body and second the leg below the hip joint. Do this for the other hip. The shoulders, elbows, and neck are done the same way too. Make the body the first constraint for the neck and shoulders, and the arm for the hands.
When you start the game engine, he should fall over like a rag doll! This concept can be applied to characters by parenting the cubes to the character mesh (like a skeleton) and using vertex groups. Though to make it look good for a detailed character you may need to use more constraints.
<- reference for game engine scripting