屌丝" seems to be a "dirty word" but also accepted and openly used. Am I missing something?
To most people the origin of 屌 is not really that clear.

KEY dictionary

2. {TW usage} swagger, be cocky/brash; be imposing, be "bad-ass"


cc c-edict

3. cool or extraordinary (colloquial)


Jay Chou 周杰伦 always goes around saying:

超屌


On Baidu there are even people who ask:

周杰伦总是说“超屌”,为什么这两个字被禁了呢?


Why is Jay Chou's “超屌” always getting censored?

So to most people 屌 just means cool...despite it's origin...and while others may think it sounds vulgar they know that is certainly doesn't not mean genitals.

As far as the origin goes this baidu user explains pretty well:

吊丝是早年李毅吧和三巨头吧互掐的时候三巨头用来骂毅丝的，之后被毅丝们用来自嘲，为什么会火，
那是因为李毅吧有内涵，号称百度卢浮宫 


basically it was just a way for people to call Li Yi's fans on 贴吧...
丝 is from 粉丝 for "fans" and well 屌 you already know...