have someone in stitches

Example: “His impression of the neighbor's cat had us all in stitches.”

Origin: "Stitch" for a sudden, sharp, localized pain — the familiar side-ache brought on by hard exertion — is an old sense of the word, and Shakespeare had already connected that specific pain to laughter by 1601: in Twelfth Night, Maria promises that if the others want amusement, they'll "laugh yourselves into stitches" following her scheme. The logic is entirely physical: laughing hard and long enough genuinely can produce the same sharp, doubling-over ache as a strenuous side stitch, so describing someone as laughing "in stitches" borrows real bodily sensation to convey just how uncontrollable the laughter has become. The specific modern idiom is generally dated to around 1930, more than three centuries after Shakespeare had already made the connection.