You are naked because you are making your way to the shower. He is sitting there fully dressed.
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Tell him to grow the fuck up and head to the shower
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Sit on his thumb with your ass cheek pushing his thumb down. Get up and go to the shower.
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Reach around and insert his thumb into your pussy realizing that quickly his thumb will be replaced by his cock. But you wouldn’t mind a quick fuck.
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Something else
I’d say number 3 and potentially start grinding x