My dad’s underpants

I had taken my roommate’s wet washing out of the washing machine and put it in the laundry basket. Shortly afterwards:

“You know those underpants of yours that you left in the laundry basket? They stunk out my washing!”

“Those aren’t my underpants. They must be yours.”

“They aren’t mine.”

“My parents were down recently. Maybe they’re my dad’s.”

“No, these have been there for weeks. Sure they’re not yours?”

“Definitely not.”

“I put my washing out on the line and it all stunk!”

“You probably just left the washing for too long before you put it out to dry.”

“No, it wasn’t that type of smell.”

I got myself a paper towel, picked up the underpants and took a cautious sniff.

“They have JAC written on them. Sure they’re not yours?”

“I’m sure!”

“They don’t even smell.”

“Get them wet, then they’ll smell!”

“My parents were down here a few months ago as well. They probably left them here then.”

“That’d be right.”

Thus the mystery was solved. The offending underpants belonged to my dad. They will be isolated and burned.