This one depends on the face.
When you use the term "uncle", it means boh style boh culture liao.
If the face looks like Andy Lau or Aaron Kwok, then you don't call them uncle, right ? So it's how you carry it.
Don't let the term "uncle" trap you. The term is now the weapon of low SES green-eyed monsters lurking in kopitiams and hawker centres. Now they alone decide who is uncle who is not. And they use it to compensate for their inferiority complex when carrying out low SES chores.