The Crab is a long established bar in the Soi Diamond itself, not the arcade. If you enter from 2nd Road it is not far down on the right hand side, almost opposite Byblos agogo.It is a large beer bar, open to the Soi. Inside there is a pool table but most people sit at the bench area outside the bar, adjacent to the Soi itself.
You can see several videos of the bar on Youtube.
Address: Soi Diamond, Pattaya, Thailand.
Crab bar website – none
Crab bar on Facebook – none