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Ok are you allowed to tell me how? Google is filled with car glitches if you put gta5 and glitch in the same sentence all you get is every YouTube video ever on car glitch.
If you have an apartment/house, there will be several things around that you can drink (whiskey, beer, wine, green drink). Make sure your character is wearing the mask you want, then go up to any one of those things and have them drink it.
Right as they start to do it, hold select to bring up the menu, go to Accessories, and quickly put on whatever hat (and/or glasses, if you want). When your character finishes, you'll now have on the mask and whatever else you tossed onto them.
Note that as missions are currently glitched and will remove any hat you happen to have been wearing, it'll revert you back to just the mask. This is only for Contact Missions, though; things like deathmatches, survival, the side activities like golf or tennis, etc. will let you retain your hat. I hope this is something they fix in the next patch.