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So a bit of background / some stats first: I'm 5'7", as skinny as a rake (I'm working on it) and I live in the UK so I'm pale as a ghost. I've always been extremely self-conscious about my body and even basic stuff like going swimming would make me anxious about how I look. I tend to wear loose fitting, baggy clothes mostly because it's impossible to find nice stuff in my size without going through the humiliation of shopping in the Teens section.
Anyway, a few months ago I happened to find the CalcSD site which talks about average sizes and you can pop in your own measurements to see how you size up in comparison. It claims the average size is about 5.5" which seems to be backed up by most of the other studies I've looked at since. I say to myself: "Well... fuck, I think I might be bigger than that" so I grab a tape measure, watch some porn and a few minutes later I have my stats (about 7" x 5.5" if you're curious). This seems.... big, like 95th %ile big. Bigger than I was expecting anyway and definitely brought a huge smile to my face. I figure I must be measuring wrong somehow so I look for something to help me compare and double check my measurements which leads me to The Visualiser where you can pop your measurements in and it'll generate a member with some objects to compare it to. Sure enough my dick looks just as big as the one on the screen when placed next to a soda can / toilet paper roll etc.
Armed with the knowledge that I'm definitely above average I made a throwaway reddit account and posted my first dick pic online. The response was overwhelmingly positive and really helped encourage me to post more. Seeing people say nice stuff about your junk is a massive confidence booster and that spilled over into my every day. I feel way more sure of myself, I'm much more likely to be flirty and all the extra confidence lead me to posting more pics / getting more positive feedback etc.
I know it's only dick pics but if it makes me feel good about myself and other people like looking at it I can't see the harm. I love being told how nice it is and knowing it's turning people on is enough to get me turned on too. Plus it's motivated me to get in shape so I can be a little more adventurous in what I post and all the pics of my skinny white chest and abs will make for a great progress timeline.
TL;DR: Finding out I have a pretty big dick is making me much more confident and now I'm kind of addicted to showing myself off.