Welcome to Bladeforums.
I have a Rat 1, but no Rat 2. But you should definitely be able to open it with one hand. Is your technique good, i.e., can you open other thumb stud knives with one hand? If so, then the pivot may be too tight. If you are up to it, you can loosen the pivot with the correct size torx bit, to that magical spot where the blade opens smoothly but there is little or no blade play when the knife is open. Use the correct flavor of Loc-tite to keep the pivot screw from moving around. But you should definitely be able to open it with one hand, with no prob.
If you are having trubba both opening and closing the knife, it sounds like the pivot screw is just cranked down too tight. So you can either adjust it yourself, or sent it back. Good luck.