Hi,
To achieve this scenario, you would need to create a Modifier (Discount Type) and ensure that you enter the item for which you need the discount to be applied in the product attribute and product attribute value fields under Modifier Summary tab. Once you save the modifier , click on Line qualifiers button and then add a qualifier of Customer for which you would want the discount to be applied. This will ensure that for this particular item and customer a discount would be applied and for other items and customers , the regular price list price would apply

Hope this clarifies

Regards
Krishna