The one about grandma's idea...

A man was walking down the street when he noticed his grandfather sitting on the porch, in the rocking chair, with nothing on from the waist down.

"Grandpa, what are you doing?", he exclaimed.

The old man looked off in the distance without answering.

"Grandpa, what are you doing sitting out here with nothing on below
the waist?", he asked again.

The old man slowly looked at him and said, "Well, last week I sat out here with no shirt on, and I got a stiff neck. This is your grandma's idea."