This method is mainly for the people who downloaded the CSS game content because they didn't have the game, if you have the game and still have this bug send me a message and I will attempt to assist you.
Now the the steps -
1. Navigate to where you have the CSS content downloaded, it should be here -
C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod\addons
2. Once there open the folder containing the CSS game content, it should look like this.
3. Once you are in there you want to open the models folder, then the weapons folder.
4. In the weapons folder, you will find a bunch of weapon files. Anything that starts with "w_" you want to delete. Anything with "v_" you need to keep.
5. Once you have done that you will want to go back to your main Garrys Mod folder and open the models folder there.
6. Once in the models folder there will be a folder named "weapons", you just want to delete that.
That's it! Go ahead and restart your game and nobody should be holding their weapons with their crotch anymore! If this didn't work for you, or you have any questions feel free to send me a PM and I will get back to you ASAP.