Confession--one time I stayed over with a date in the next town over. I had planned on going home. Since I had plans with a friend that next day, I literally went to Kohls at 8am and bought new clothes.
Not quite the same, but I was in a training class years ago. There was a guy in there who wore a suit every day. One day I happened to notice he had the same tie on from the day before. Then at some point I noticed an line of pen ink on the cuff of his white shirt. And I saw the same line the next day and the next.
It was clear he was pretty much wearing the same ENTIRE outfit every day. The suit - if you're broke, ok, I get that, I guess. But the SHIRT?? Ew.
Maybe you could just 'jokingly' give him some advice to keep some fresh clothes in his car and see If that breaks the seal for him to tell you what happened.
Yeah, I think I'll wait until he has a little coffee in him, and then ask, "So how was last night?"
I'll report back on how much info he ponies up
PS - I like to live vicariously through some coworkers. The extent of my excitement last night was letting DS watch both the Mickey Mouse ClubHouse and Yo Gabba Gabba. We live on the wild side...