Dem lot
Them. That crowd over there. The Dublin plural, filed alongside yer man and yer wan.
I'm not sittin' wit dem lot, dey ate all de sangwiches last time.

Shall I translate it into posh English for you, batman?
Oh, hello! I didn't see you come in. Here it is in posh English.
I decline to be seated with that party. On the previous occasion they devoured every last sandwich.
Questions
What does dem lot mean in Ireland?
Them. That crowd over there. The Dublin plural, filed alongside yer man and yer wan.
How do you use dem lot in a sentence?
“I'm not sittin' wit dem lot, dey ate all de sangwiches last time.”
Updated
On the list: Irish slang words