Chaim Grade, considered by some to be the finest Yiddish novelist of all, was a former yeshiva student in der Lita. His two-part book 'The Yeshiva' is a historical fiction that portrays persons such as the Chazon Ish and R. Aharon Kotler under different names. It is a very interesting book.
In 'Volume II: Masters and Disciples' he writes about American bochurim in the Mirrer Yeshiva
...a group of students had recently come from America. The Americans had money but not a crumb of decorum. In the beth medresh they hung their coats on other people's hangers and threw their galoshes about. There was a fine of at least ten groschen for breaking the ruls, but the Americans laughed and paid twenty. They went around with open jackets and unbuttoned collars. Polka-dotted ties dangled from their necks. They weren't ashamed to hitch up their trousers in public and jingle coins in their pockets. When it was hot they simply took off their jackets. They wore their caps pulled down low over their hard heads, their thick, disheveled shocks of hair hanging down to their eyes. They spoke with chewing gum in their mouths. The Americans found it right and proper to shout to one another, "Hey Jack! Hey, Joe!" and they boxed in middle of the street, jumping around like goats. It wasn't surprising that when an older Mir student saw this, he was so ashamed that he didn't know where to hide.
Of course this is a fictional portrayal, but there is obviously a grain of truth to this, at least a grain of truth in that this is roughly how these young American whippersnapper bachurim were viewed. Its kind of interesting to see that teenagers are teenagers, and even if some of these very same guys called Jack eventually grew up and became serious and wore a beard and kapote and maybe even became some of the latter-day gedolim, or are of those circles.