Question: Why did Geno break Mark's nose at the end during the party?
Question: What kind of dog is Lucky supposed to be, a mix breed or collie mix?
Answer: Lucky is a mongrel mix. A mix of 2 breeds. A quick search suggests a possible terrier and lab mix.
Answer: Geno deliberately broke Mark's nose during the party after Mark made a snide remark. After the party, when Mark suggested a way to have John committed and still get their money, Geno had enough of Mark's ignorance and punched him in the nose again to add further insult to injury.