Known as 'grab your dick and double click' or even 'GUDNDC' (grab ur dick n double click).
Basically, it consist on grabbing your firehose while seeing porn on the internet... sometimes causing you to use ur left hand to move the mouse around cause you are stroking usin' the right hand (if you are left handed, it causes you to use right hand to drive your mouse)
To do GYDADC in centain places such as internet cafes, friend's houses or at school, represents a high risk only pros can avoid (needless to say its better not to sake hands with a GYDADC pro).
Notice down at the example how can GYDADC be used as a verb.
Some one who has no room for anything in life except the gym. They live, sleep and breathe the gym making them unbearable to have a conversation with.
They are so 2 dimensional that they will always try to steer the conversation towards fitness because they know nothing else.
These are different to Gym enthusiastic who will par-take in lots of different exercises outside the gym such as rock climbing or swimming.
"Today I bench 150kg and squatted 200kg, and oh man the funny part was the ladies, man you should have seen this. The ladies clearly didn't want there boyfriends no more. Why would they when they can have me? "
"No one likes a gymdamentalist. Don't be a douche!"