// Rotate a button 10 degrees clockwise when presed.

private var rotAngle : float = 0;
private var pivotPoint : Vector2;

function OnGUI () {   
    pivotPoint = Vector2(Screen.width/2,Screen.height/2);
    GUIUtility.RotateAroundPivot (rotAngle, pivotPoint); 
    if(GUI.Button(Rect(Screen.width/2-25, Screen.height/2-25, 50, 50),"Rotate"))
        rotAngle += 10;
} 

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    private float rotAngle = 0;
    private Vector2 pivotPoint;
    void OnGUI() {
        pivotPoint = new Vector2(Screen.width / 2, Screen.height / 2);
        GUIUtility.RotateAroundPivot(rotAngle, pivotPoint);
        if (GUI.Button(new Rect(Screen.width / 2 - 25, Screen.height / 2 - 25, 50, 50), "Rotate"))
            rotAngle += 10;
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    private rotAngle as single = 0

    private pivotPoint as Vector2

    def OnGUI():
        pivotPoint = Vector2((Screen.width / 2), (Screen.height / 2))
        GUIUtility.RotateAroundPivot(rotAngle, pivotPoint)
        if GUI.Button(Rect(((Screen.width / 2) - 25), ((Screen.height / 2) - 25), 50, 50), 'Rotate'):
            rotAngle += 10