Looking for both logical and emotional reinforcements, from casual acquaintances to intimate partners, and any orientation if not especially, everyone matters.
Frame it as a “friend” if you’d like, but I would like to know what made an impactful impression on you personally, above and beyond any hypothetical.
Typically, if someone has a body “flaw”, they know about it. Lying will quickly be shot down and disregarded. For example, if you tell an overweight person that they are thin, they’ll know it’s not true, and they won’t accept it. Tell them they have a nice butt (if the context is appropriate) and they’ll remember and appreciate that.
Avoid making them the direct object in a compliment.
“That outfit makes you look good” implies that they didn’t look good until they put on the outfit.
“You are looking good.” gives the compliment to the person, not the attire.
Also “that looks awesome on you” says you and the outfit both look good.