That was a left-handed compliment about my new haircut.
left-handed compliment
idiomA complimentary remark which is ambiguous or ineptly worded, so that it may be interpreted as having an unflattering or dismissive sense.
She told me I looked great for my age, but it felt like a left-handed compliment.
His remark about her sudden promotion was clearly a left-handed compliment, implying she only succeeded because of her connections.