It mesns f.u.
More literally "go do it in your a-- (other word for 'donkey'.)
Explanation:
Ba fungu
Ma fungoo
Va fangu
(etc etc etc)
Are all variations on one theme: what the Italian expression "va' a fa' 'nculo" sounds like to sn English speaker.
The expression isn't "proper" Italian, anyway.
It has been assimilated into the Italian language (spelled as "vaffanculo" or "va a fanculo", and I hope that it doesn't get auto-censored. It sure does on Italuan Yahoo)
but the original " va' a fa' 'nculo" is actually Neapolitan, a language spoken in most of southern Italy, with many local dialects so different that it can be hard to understand each other, at first.
Before mass media taught everyone to speak proper Italian, sime 50 years ago, most people could only speak the local dialect of a local language, especially in rural areas... but I'm drifting off topic.
"Ba fungu" is a mispelling of "va fanculo", and it means f.u.