WordPress Recent Comments Widget exclude own comments

You could try this to skip comments made by user with user_id = 1 in the Recent Comments widget:

add_action( 'widgets_init', 'custom_recent_comments' );
function custom_recent_comments(){
    add_filter( 'comments_clauses', 'custom_comments_clauses' );
}

where

function custom_comments_clauses( $clauses ){
    $clauses['where'] .= " AND user_id != 1 "; // EDIT
    return $clauses;
}

In a similar way you can target the user email with:

$clauses['where'] .= " AND comment_author_email != '[email protected]' "; // EDIT

This will affect the where part of all the comments queries made after the widgets_init hook.

PS: If you only want to run the where-filter once after the widgets_init hook, you can use this modification of the custom_comments_clauses() function:

function custom_comments_clauses( $clauses ){
    remove_filter( 'comments_clauses', 'custom_comments_clauses' );
    $clauses['where'] .= " AND user_id != 1 "; // EDIT
    return $clauses;
}