About all the yorkies I've had had sat like that or funnier
granted my current girl has luxating patellas and she actually sits more on her hips than butt, though when she was younger and weighed less she sat directly on her butt. She'll do it occasionally every so often.
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R.I.P. Mick & Mandy (before 2010), Mila - 4/3/15, Chloe - 2/18/16, Kimchi - 6/2/2021