"Spouting off" is a verb, not a noun.
I think it's "you." Maybe it's an idiom. It's like the person is pointing a finger at him (at you). More at him than what he said.
Sorry, SB, it may be a verb but it is functioning as a an apposite, a noun phrase, in this case, placed after a noun providing further information about the noun.
What you have is:
You: a pronoun as the subject of the sentence
spouting off like a New York cabbie: an apposite noun phrase adding information about the subject
could cost: the verb of the sentence
a lot of people their jobs: a noun phrase as the direct object of the verb
Technically, and you probably don't want to hear this, you should enclose the appositive in commas. The phrase is providing non-essential information. Enclosing it in commas would indicate the start and end of a detour your sentence goes on in between the subject and its verb.
This is what CMOS says at 5.21 Appositives defined; use
An appositive noun or noun phrase is one that immediately follows another noun or noun phrase in order to define or further identify it — for example, George Washington, our first president, was born in Virginia ('Our first president' is an appositive of the proper noun 'George Washington').
Commas frame an appositive noun or noun phrase unless it is restrictive — for example, compare Robert Burns, the poet, wrote many songs about women named Mary ('poet' is a nonrestrictive appositive noun) with the poet Robert Burns wrote many songs about women named Mary ('Robert Burns' restricts 'poet' by precisely identifying which poet).
A restrictive appositive cannot be removed from a sentence without obscuring the identity of the word or phrase that the appositive relates to.
I could not understand what you meant the first time I read the sentence: I needed a lengthy double take to figure it out. I know you work hard to eliminate commas that would be required in formal writing - and I agree it makes for better fiction - but I sincerely suggest they are necessary in this sentence to assist readers' comprehension.
The comments above suggesting 'You' be replaced with 'Your' and 'You're' are valid, but not right for the accusing tone of the meaning you are looking for.