What it means
A hoot is someone or something that's seriously funny and dead good value. You'd call a person a hoot if they've always got the room cracking up, or say a night was a hoot if it turned out way more fun than expected. It's a bit old-school, yeah, but still lands as a warm compliment.
Usage examples
"Your gran’s an absolute hoot. She had the whole pub howling, even Dave the misery-guts, chatting about the postie like it was a true-crime doc."
"Your nan is an absolute hoot at parties, she had the whole room in tears with her karaoke."
"The team-building day sounded grim but it turned out to be a right hoot, we still talk about it."
"That quiz night was a proper hoot once Kev started cheating off his own girlfriend and still came last."
"She's a hoot on a night out, five minutes in and she's got strangers laughing at stories about her dodgy first job."
Where it comes from
Hoot first meant a loud cry or shout, and pretty early on it got tied to bursts of laughter too. By the late 1800s in English, a hoot was being used for something wildly funny or entertaining, the kind of thing that sets everyone off laughing.