Players can roleplay with each other, or they can roleplay against each other. The former lends itself to creating great stories filled with interesting people. The latter is just a good way to amuse yourself if the campaign sucks.
Brace yourself, Sweetheart! I have "Improved Stamina."
There is a reason you're supposed to railroad the player characters together via the classic "tavern meeting": Most players are selfish and unruly and likely to kill each other with their attempts at roleplaying.Besides, that sort of thing just distracts everyone from the story you're telling.
