What a poor attempt at a joke! A battleship coming down the *street*? Surely the 'joke' works just as 'well' if the proposed scenario were credible e.g. "How would you react if you saw a *tank* coming down the street?" i.e. the punch-line is the would-be sailor making a wise-crack against the fact that expecting a serious response to pretend threats is daft. As written, there's room for doubt; the wise-crack could be aimed at the lack of credibility to the scenario the psychiatrist proposed. After all, I thought the would-be sailor was going to remark upon the 'ship on the street' notion. Yet when I read that lame 'punch-line' (that could have substituted a tank) I was perplexed!