Jack Carter: Frank wasn't like that. I'm the villain in the family, remember?
Jack Carter: You couldn't run an egg and spoon race Eric.
Eric: So, what're you doing then? On your holidays?
Jack Carter: No, I'm visiting relatives.
Eric: Oh, that's nice.
Jack Carter: It would be... if they were still living.
Edna: What's that gun doing in your room? Suppose I phone the police, told them there's a bloke in my hotel... who's planning to shoot somebody?
Jack Carter: You wouldn't do that.
Edna: How do you know I wouldn't?
Jack Carter: 'Cause I know you wear purple underwear.
Edna: What's that supposed to mean?
Jack Carter: Think about it.
Jack Carter: You know, I'd almost forgotten what your eyes looked like. Still the same. Pissholes in the snow.
Peter: Don't let us interrupt you.
Jack Carter: Now.
Jack Carter: Goodbye Eric.
Answer: It's a show of sophistication. Working class men in pubs and clubs (north, south, and London) typically drank from beer mugs. By insisting on a thin glass Jack is making a public display, of socially distancing himself from the average beer drinking peers, showing he has refined himself from his working class roots.
This is 180° wrong. Thick pint pots with handles were just becoming fashionable when this was made, by ordering a straight "thin" glass he is opting for traditional over trendy.
This is 100% rubbish. The new design of the dimpled mug glass in the 70s was a continuation of the fluted mugs of the 1920s. Northerners, particularly Yorkshire, preferred their beer in jugs, not straight glasses.
Not true at all: everyone I knew in the 70's and 80's always preferred their beer in a normal "thin" pint glass, not the thick, chunky dimpled things. Rightly or wrongly, we always felt it tasted better from a proper glass.