Read this:
Crack
What did you think of? A window crack or the drug?
Read this:
Crack
What did you think of? A window crack or the drug?
Okay, so the joke is playing on the word "crack" which can mean either a split in somethin' like a window, or the illegal drug. The joke is askin' you what you thought of first when you read the word. This is funny 'cause you're probably addicted to the internet since you're readin' this.