collision enter

how would i define a collision enter with any game object?

The manual page has example code for C#, JavaScript, and Boo. Put the code in a script on the object that's detecting collisions.

Note that "any" game object is limited to "all objects that have a collider component on them." If there's no collider, then no collision is detected. Also, the manual stipulates that one of the bodies must also have a rigidbody component.