Overnight sleeper

[rebbonk]

A man was in an overnight sleeper train. He got onto the top bunk, then at the next stop a woman got on the train and lay down on the bottom bunk.

It was a cold night, and eventually, the woman speaks; "Can I borrow a blanket please?"

The man replies, "I've got an idea; why don't we pretend that we're married?"

The woman, giggling, says, "OK then"

"Great", the man says.

Spoiler:

"Get your own blanket!"