Wife was at work, I was decorating a house we were moving into. I'd ad a shower as we finished up and normally just the wife and me I didin't close the bathroom door. Sister-in-law walked in as I was towelling down, she watched for a minute then went to another room to change. After a minute I followed her, she was just pulling her jeans down. She sensed I was there, turned and rather than strip to bra and panties before redressing she continued until she was naked. We stood close each other, she shook my cock like you would someone's hand, I felt her tits and nipples. We agreed it was a bad idea,
Next day we used the same room to get changed and fucked before we started decorating.