Just a simple snippet that will let you display the currently logged in users avatar. Just place this snippet within a template file in the location you wish to display it. Also notice that you can change the avatar size with width and height but also class.
echo bp_core_fetch_avatar( array(
'item_id' => bp_loggedin_user_id(),
'width' => 50,
'height' => 50,
'class' => 'avatar',