Green’s Dictionary of Slang

(Irish) a very great fool.

1981		J. Pepper Ulster-Eng. Dict. on Images from Ireland 🌐 buckijit, extreme type of idiot: ‘That man’s nathin but a buckijit.’ ‘I’m not going to the match the day. The goalkeeper’s nathin but a buckijit.’.
1985		Van Morrison ‘Boffyflow and Spike’ Story on sleevenotes of Sense of Wonder [album] Boffy is covered with leaves completely the buckijit and Spike is in hysterics.