The following is the list of hooks used by Frank Bultge’s plugin Remove Comments Absolutely:
# Set the status on posts and pages - is_singular ()
add_filter( 'the_posts', array( $this, 'set_comment_status' ) );
# Close comments, if open
add_filter( 'comments_open', array( $this, 'close_comments'), 10, 2 );
add_filter( 'pings_open', array( $this, 'close_comments'), 10, 2 );
# Change options for dont use comments
# Remove meta boxes on edit pages
# Remove support on all post types for comments
add_action( 'admin_init', array( $this, 'remove_comments' ) );
# Remove menu-entries
add_action( 'admin_menu', array( $this, 'remove_menu_items' ) );
# Add class for last menu entry with no 20
add_filter( 'add_menu_classes', array( $this, 'add_menu_classes' ) );
# Remove areas for comments in backend via JS
add_action( 'admin_head', array( $this, 'remove_comments_areas' ) );
# Remove comment entry in Admin Bar
add_action( 'wp_before_admin_bar_render', array( $this, 'admin_bar_render' ) );