Meaning and local context
In Chicago, “jagoff” means An annoying, foolish, inconsiderate, or objectionable person. Used in Chicago and also strongly associated with Pittsburgh.
Example in context
A local example is “Some jagoff blocked the whole doorway.” In plain English, that means “An inconsiderate person blocked the whole doorway.”
Some jagoff blocked the whole doorway.
An inconsiderate person blocked the whole doorway.
How to interpret it
The surrounding sentence is important when interpreting “jagoff”. Use the regional sense above when the situation matches the example instead of relying on the word or phrase in isolation.
Tone and caution
It is an insult and may cause offence. Because this is informal regional language, tone and situation should guide whether you use “jagoff” yourself or simply recognise it when someone else uses it.