Green’s Dictionary of Slang

Patty Hearst n.

also Pattie
[rhy. sl. = SE first; ult. US heiress-cum-urban terrorist Patty Hearst (b.1954)]

a first-class degree.

[UK]R. Puxley Fresh Rabbit.
[US]J. Burkardt ‘Rhyming Sl.’ Wordplay 🌐 Pattie Pattie Hearst a first (university degree).