This really is a very interesting question. Chess is a game, a social activity, and like other social activities it has developed conventional manners players are expected to follow.
However, the rules of chess have been purposely constructed and refined so that by playing to win—or, if one cannot win, at least to draw—you support rather than contradict the conventional manners of the game.
In your case of perpetual check, the implicit question regards which of the two of you, whether the checker or the checked, has the responsibility to yield. In chess, the long-settled convention is that the checked has the responsibility to yield. Indeed, as another answerer has noted, the very rules of the game have evolved to support the view that the checked must yield. Indeed, the explicit rules are even better than that, for the checked need not do anything but respond to checks a few times, after which the threefold-repetition rule comes into effect and the game is a draw.
This is normal, perfectly conventional play in chess. Actually, like the pin and the fork, the perpetual check is kind of a cool maneuver; you have to be aware that a losing opponent might do it to you, and you have to guard against this if you can. Perpetual check (formally, a threat of threefold repetition) has already been done this very year in the FIDE Candidates tournament, and was also done in recent years during a World Championship match. No one thought anything of it: each perpetual check was just a normal, polite, standard draw.