Disallow HTML in textbox and textarea fields

You can use this hook “xprofile_field_data_updated”. This hook is called just after updating the field value. Something like this:

function custom_xprofile_profile_field_data_updated($field_id, $value) {
    $field = new BP_XProfile_Field($field_id);
    if ($field->type == 'textbox' || $field->type == 'textarea') {
        xprofile_set_field_data($field_id, bp_displayed_user_id(), strip_tags($value));
    }
}
add_action('xprofile_profile_field_data_updated', 'custom_xprofile_profile_field_data_updated', 10, 2);

This function is deleting tags from all texboxes or textareas fields.