When I was in my late teens, my friends and I couldn't afford to go out drinking in town all that often (and some of our friends weren't 18 yet, which also made things difficult) so my best friend Jake used to invite me and 3 or 4 other guys around to his house on a Friday night. We'd order a pizza, play xbox and drink a few cans of beer. We'd usually stay overnight and sleep on the sofa.
One night, it was just me, Jake and his older brother (not sure why the other guys weren't there, maybe they had been busy or had left early). A couple of hours into the evening, Jake's brother invited a couple of girls over. I knew one of them because she had been in my tutor group at school, she was a slim blonde girl that I'd had a crush on when I was younger. The other girl, the one I didn't know, was her friend - I can't remember her name, so I'm just gonna call her Lucy.
Jake's brother fancied the fuck out of Lucy, hence inviting her over that night. Not sure what he saw in her... she was pretty cute, but nothing compared to her friend (the blonde I knew from school). Lucy must have been a couple years older than me, maybe early 20s, sort of thickset but not fat, with medium sized boobs and long straight black hair (not dark brown, but actual black, it was probably dyed). Can't remember what she was wearing, it was a cold winter evening so probably jeans and a jumper or something, certainly not anything sexy or revealing.
Both girls were planning to stay the night - they had both brought their pyjamas - and I remember being pretty excited about seeing the blonde girl in her nightwear. Unfortunately, she never got changed, and around midnight she called her dad to come pick her up and take her home. Bummer

Anyway, Lucy did stay over. She wasn't drinking, but she was loud and bubbly, had a real good sense of humour. She and Jake's brother really hit it off. Jake's brother invited her to sleep up in his room rather than on the sofa with me and Jake (bummer again, lol). Lucy went into the bathroom to change into her pyjamas, whilst Jake's brother went upstairs to his room to "change the bedding" (in reality, probably to clear up all his dirty underwear and fap-rags and stuff).
When Lucy came out the bathroom, she was wearing a pair of baggy tracksuit bottoms and a tight vest top. Obviously she wasn't wearing a bra, there was a little bit of sag to her boobs. There was a gap between her bottoms and top revealing her belly button, it was an outie. I clearly remember that she kept pulling her bottoms up above her waist, but they kept dropping slightly to show her cute little outie. I remember being a bit turned on by this - she kept chatting to us as normal, but she'd keep tugging her bottoms up every couple of minutes or so. Lucy obviously knew that Jake and I were checking out her navel at every opportunity, because she mentioned that although her friend had a belly button piercing, she couldn't get one because of her outie.
Jake's brother shouted to Lucy from upstairs ("the bedroom's ready", or something like that). Lucy leant over to pick up her overnight bag from beside the sofa, revealing the top of the crack of her (fairly wide) butt. She straightened up, her bag in one hand and a glass of water in the other. She turned to Jake and said good night, then turned to me to do the same. I was sat on a low bean bag, so my face was about level with her cute little belly button.
Like I mentioned, seeing her navel - although it's a pretty innocent part of a person's anatomy - was sort of arousing. I can only assume Jake felt the same, or guessed what I was feeling, because he stepped up behind her, crouched, and pulled down her tracksuit bottoms to her knees. He didn't do it particularly quickly - I'm not sure if I'm just remembering it this way now, but it was like in slow-motion. Lucy wasn't wearing any underwear.
I can still clearly picture Lucy, standing there, holding a glass of water in one hand and her bag in the other, her tracksuit bottoms around her knees, in a sort of shocked silence, for what seemed like five whole seconds.
Then she squealed, and dropped the glass of water (but not the bag - I guess in her panic she knew she had to drop SOMETHING and didn't care which) and covered her crotch with her hand. I sort of squealed too (yeah, not my proudest moment, lol) and then shouted at Jake, "What the fuck, man?!" and I made a big thing of looking away, trying to be a gentleman.
Still, that image of Lucy... wow! She hadn't been wearing any underwear, and my face had been pretty much level with her navel, less than a foot away from me. She was shaved, but with a little bit of stubble. She had prominent inner lips which stuck out slightly, darker than her outer lips, and they clung to one another. I remember one lip was slightly longer than the other. I can also remember very clearly thinking to myself, incredibly stupidly, as though it was some universal truth, "Wow, outie belly button = outie pussy," even though I wasn't that naive even back then.
Lucy was mortified. Her whole face was red. I think she was too embarrassed to be angry (though she had every right to be). She put her bag in front of her crotch, then bent over to hoist up her tracksuit bottoms with her free hand, just as Jake knelt down to pick up the glass she'd dropped (to get an eyeful from behind, I guess). Then she started apologising for squealing! Jake apologised for being a dick and said that he had expected her to be wearing underwear, and I pretended to be angry with Jake for being so immature. She wouldn't make eye contact with me, maybe because she knew I'd seen all her goods up close. Jake fetched her a fresh glass of water, Lucy told Jake not to tell his brother, and she scurried upstairs.
Jake's brother came down shortly after. He seemed a bit confused, convinced he was on to a sure thing that night with Lucy in bed, only to be told that she was tired and wanted to sleep. Jake burst out laughing and told him what happened. I actually felt a little sorry for his brother, he was upset that Jake had given me an eyeful of the girl he fancied before he'd even seen her naked. Jake kept ribbing him, saying he'd seen her dangling lips from behind as she bent over. Jake's brother got really sullen so I didn't stay much longer, and walked home.
I think Jake's brother did hook up with Lucy after that night, but I don't remember how long it lasted (it wasn't long). But I do remember that Lucy's pussy was the subject of my conversations with Jake for weeks afterwards!