Translation:Good morning, Uncle.
Problem is, おじさん doesn't necessarily have a filial tie with ya. A random midlife-crisis'ing dude that you see every day or so can be affectionately called an おじさん, and it's weird to call them uncle in English.
It caused A LOT of confusion for me too:
伯父(さん) = おじ(さん) = oji(san) = uncle (anyone older than one's parent)
伯母(さん) = おば(さん) = oba(san) = aunt (anyone older than one's parent)
お祖父さん = おじいさん = ojīsan = grandfather
お祖母さん = おばあさん = obāsan = grandmother
祖父 = そふ = sofu = grandfather (informal)
祖母 = そぼ = sobo = grandmother (informal)
お爺さん = おじいさん = ojīsan = a very old man
お婆さん = おばあさん = obāsan = a very old lady
As you see, お祖父さん + お爺さん and お祖母さん + お婆さん are pronounced the same. Therefore, by writing them with katakana, you leave it open whether it's your ancestor or just an equally old person.
It was a joke. I don't expect to go to Japan anytime soon and if I do I hope I won't get into a brawl and if I do I hope that I can pick it well enough that I can win it and if I don't I hope I'll know a better way to announce that I give up and if I don't then I deserve it.
No, when you learn a language, it's best to forget everything you know and try hard not to relate your language to that one. Many of the things you know-- phrases, metaphors, idioms etc. do not exist in that language at all; only core philosophies such as desire, hunger, thirst etc. are shared by all.
saying "uncle!" is specific to North America and is, as far as i understand, not even said in other english-speaking countries as an idiomatic expression
If you don't know what "say uncle" means, here's the wiki: https://en.wikipedia.org/wiki/Say_Uncle
Furthermore, even in the U.S., saying this will not help you in a real fight, as this phrase is typically used for low-level fights which lack the intent to kill (such as wrestling or fighting with siblings) and it's usually brought up by the person winning as an offering of mercy
"Say 'uncle' and i'll let you go."
About the distinction between おじさん and おじいさん (uncle and grandpa), how would you be able to tell the difference in normal speech, since they sound similar? Let's say you have an uncle and a grandpa both living in Osaka, and a stranger just asked you, ”おおさかのおじさはおげんきでか?” (How is your uncle in Osaka?), so context is not of much help.
The difference is in the pronunciation of the extended vowel. In おじいさん you hold the い sound for longer. It helps to compare it to musical notes. A normal vowel from the じ in おじさん is like a quarter note. You hold it for one beat. The extended じい in おじいさん is like a half note, which you hold for two beats, or twice as long as a normal vowel sound.