The window lock on many RVs where the windows slide sideways can be defeated. If the window latch looks something like a wing-nut, where you push on one side to lock it and then on the other side to unlock it - you can place both palms on the window pane that slides (near the divider between both panes), push the window inwards about 1/8 inch to 1/4 inch, then while it is pushed in you slide the window open.
For the above to work you have to know what type of latching mechanism that the window has in place.