BuddyPress.org

At the moment, there is no easy way to turn off Gravatar. I agree that there should be an easy way, as there can be performance concerns, as @mistercyril. (Though I find “I’m starting to think I’m the only one concerned with performance” unnecessarily confrontational.) I’ve had issues with it in the past myself.

I’ve just opened a ticket to make disabling Gravatar easier: https://trac.buddypress.org/ticket/2697 Until it’s been implemented, here’s the general core-hack strategy for disabling Gravatar altogether:
1) In bp-core/bp-core-avatars.php, find where the $defaults for bp_core_fetch_avatar() are set. Change
`’no_grav’ => false,`
to
`’no_grav’ => true,`

2) There will likely be some instances where the Mystery Man doesn’t kick in properly (group avatars, existing users). Write a filter for `’bp_core_fetch_avatar’` that sets the avatar to some default value when no avatar is returned.