Since the topic has come up, one way to reduce collisions with all geolocation turned off would be to request the user tap a certain key (or even two keys in succession) with the phone instead of just the space bar.
Or presumably tap the spacebar twice (or more) - giving an interval for matching - which would avoid having to consider key positions and mishits and alternate keyboards and such.
Or better yet, tap out your Bump login and password with the phone!