"Julio and I" vs "I and Julio" [duplicate]

Possible Duplicate:
“My friends and I” vs. “My friends and me” vs. “Me and my friends”
Is naming the first person last proper grammar or just proper manners?

"Julio and I went to the schoolyard." is a valid sentence.

How about "I and Julio went to the schoolyard."?

It's impolite (putting yourself first) and awkward, but is it grammatically incorrect?

[I realize the original lyric "see me and Julio..." is a grammatically correct imperative sentence]

It's impolite (putting yourself first) and awkward, but it is correct grammatically.

I don't think "I and Julio went to the schoolyard." is grammatically incorrect.
It is simply not the common (and polite) form.

See for instance the personnal pronoun section on compounding:

When a personal pronoun is connected by a conjunction to another noun or pronoun, its case does not change.
We would write:
"I am taking a course in Asian history"; if Talitha is also taking that course, we would write:
"Talitha and I are taking a course in Asian history."
(Notice that Talitha gets listed before "I" does. This is one of the few ways in which English is a "polite" language.)

The same is true when the object form is called for:
"Professor Vendetti gave all her books to me"; if Talitha also received some books, we'd write:
"Professor Vendetti gave all her books to Talitha and me."