what does "but still"mean?
Any man, she thought, studying her copy of the sketch yet again, with a thin face, long, somewhat shaggy medium brown hair and thin lips.
She couldn’t swear to the lips, if it came to that. Had they really been thin or had she projected thin lips because he’d struck her as such a tight-ass?
So much for her powers of observation, she decided in disgust, which she’d considered above average before this.
Of course, there wasn’t any proof her tight-assed, tonic-and-lime-drinking customer had anything to do with anything. But still.

Question

what does "but still"mean?
Any man, she thought, studying her copy of the sketch yet again, with a thin face, long, somewhat shaggy medium brown hair and thin lips. 
She couldn’t swear to the lips, if it came to that. Had they really been thin or had she projected thin lips because he’d struck her as such a tight-ass? 
So much for her powers of observation, she decided in disgust, which she’d considered above average before this. 
Of course, there wasn’t any proof her tight-assed, tonic-and-lime-drinking customer had anything to do with anything. But still.

Answer

Nevertheless, even so -- referring to the previous sentence.

Answer

Another example: Mark: Sara shouldn't eat so much junk food. It isn't good for your health. -- Tim: Are you kidding? Look at her. She works out every day and is so fit looking. -- Mark: But still. = Nevertheless. = But despite her fitness, she should still eat healthier.

Answer

But still means even so.

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