One in the baby maker, three in the brownie baker
One finger (primarily a thumb) in the vagina, three fingers in the butt-hole
Dude I was so drunk and she was so horny, so I for some reason put "One in the baby maker, three in the brownie baker" - This term was originally coined in a drunk-dial voicemail to a special friend after a night of drinking and after-partying in a hot tub with a naughty french girl.