That 'I have always liked Cowabunga' scene makes no damn sense, either in the movie or here. 'Cowabunga' ain't a descriptive term; it's something you yell when charging into action. What Splinter is basically suggesting that they say is 'we were Cowabunga', which is like saying 'damn, we were Geronimo back there', or 'dudes, we were totally Banzai'. It's a shame, too, because otherwise, the ending sequence is pretty effective.