So my friend and I played a quick round today and he made a green maneuver to lose a stress token, but in making that green maneuver, he bumped his own ship.

Now, does a bump mean that his movement is stopped at the base of his other ship, and the green maneuver he was performing was not completed? That would leave his ship with the stress token? Yes?

His argument was that the green maneuver was initiated allowing him to remove the stress token, but he still lost his action from the bump. Is that right?

Your friend is correct, he loses the stress and also his action, as per normal overlap rules.

Alright, thank you.

Attempting a green will cause a loss of stress even if the maneuver isn't finished.

Similarly a Red maneuver will cause stress even if it can not be completed.