The arguments that soundly defeat all the pure forms of psychological egoism are available in the criticism section. The guy who lays down in front of the tank isn't being selfish in any reasonable sense of the word, and most attempts to rescue the claim end up trivializing it, by simply calling any goal-oriented behavior "selfish", even when those goals are clearly not for one's own benefit.

There are more defensible forms of psychological egoism, but your summary ("there is personal benefit (feeling good) to being altruistic") doesn't work.