The right place on rare stylus using games, and I chew on it during games with massive stylus requirements, IE Brain Age.
Same, for games that don't need the stylus much. I caught myself sticking it in my mouth when playing a stylus-heavy game and needing to do something else / move for a sec the other day (yay Meteos, best damned purchase I've made all year). Thought it was kinda weird, but apparently notWhere is other? I just hold mine in the space between thumb and forefinger whilst holding the ds.