As far as my understanding: Boy-o reflects one's behavior while it can also be used to address a group of males. But Guy seems to be mostly used in addressing the people while it is less used as a behavioral word.
Please suggest what should I use and when.
Here are some examples I thought of:
Usage : Boy-o
1). How's it going boy-o?
2). That particular stare has the boy-o in it. (I think it makes more sense)
Usage : Guy
1). He's a nice guy.
2). The kids asked passing workers for pennies for the guy.
Also, I think Boy-o seems to be informal as compared to guy.
Looking for an appealing noun to address a group of people.
EDIT:
Boy-o reference: Strangers in Death
Best Answer
"Boyo" is a non-standard word that simply means "boy":
As the dictionary entry notes, it is "Irish" and the most common place to hear "boyo" is from Irish mob stereotypes in film or television.
As for your examples:
(1) would be correct, (2) seems wrong to me replacing "boyo" with "boy" doesn't really make sense in this context -- but I have to admit that I am not an expert on the word's usage.
"Guy", on the other hand, is extremely common and your examples are accurate usage.
"Guy" is extremely informal. "Boyo" is mostly reserved for Irish stereotyping so I would avoid it. Neither word refer to a group of people unless you pluralized them. If you did, "guys" would the most appropriate term:
There is a question about the applicable gender of guys but boyos would most probably refer to a group of lads only.