Get on garry's mod and play on a map and don't change it until you open the menu up 100,000 times.
This is a quick guide to farm this achievement. You create a simple alias loop that will rapidly open and close the menu.
- Open Garry's Mod in window mode (Options > Video)
- Start a map in sandbox mode (gm_flatgrass will do)
- Type the following into console
- alias menuloop "+menu;-menu;menuloop"
- Wait about 10 minutes. The game will be lagging or "not responding" due to the loop. Since you put the game in window mode you can do something else on your computer while you wait.
- Close Garry's Mod (you will probably need to force close it).
- Open Garry's Mod and you will received or have already received the achievement. If not, you didn't wait long enough.