wp_delete_comment takes two tries to delete - then deletes all comments

The Insecure Way

You need to change your form so that it includes the ID of the comment you want to delete, e.g.:

<form method="post">
  <input type="hidden" name="comment_id" value="<?php echo get_comment_ID(); ?>" />
  <input type="submit" name="btn-delete" value="try-delete"/>
</form>

Without this, you have no idea which comment the user wanted to delete.

Then, you need to move the code that deletes the comment to a hook in functions.php e.g.:

add_action( 'init', 'i_am_not_safe_to_use' );
function i_am_not_safe_to_use() {
    if ( is_admin() ) {
        return;
    }

    // only run if we're deleting a comment
    if ( empty( $_POST['btn-delete'] ) || empty( $_POST['comment_id'] ) ) {
        return;
    }

    // TODO, security checks

    // delete the comment
    $comment_id = intval( $_POST['comment_id'] );
    wp_delete_comment( $comment_id, true );
}

This will work however it is insecure! Now anybody can delete any comment they want by submitting the form!!!

Security

The code needs to also do the following:

• check that the user has the necessary capability required to delete that comment
• add a nonce to the form
• check the nonce in the hook

At a minimum, you need this check:

if ( current_user_can( 'moderate_comments' ) || current_user_can( 'edit_comment', $comment_id ) ) {
    // then the user has permission to delete the comment
} else {
    wp_die( 'sneaky hackers! You are not allowed to delete this comment' );
}

The REST API

If you send an authenticated DELETE request to the comments REST API at yoursite.com/wp-json/wp/v2/comments/<COMMENT ID GOES HERE> then refresh the page, your comment will be gone.