A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

talk big • talk small
talk big —(coll.) speak boastfully (also: talk large): “I hate to
talk big,” I said, “but I’m not afraid of Steelgrave or a dozen
like him in one package.”
talk small —(also: talk small talk) make conversation about
unimportant things: We talked small for awhile, avoiding the
obvious topic at the fore of each of our minds.
Note: 
The expression does not correlate in meaning with the
phrase sing small—(coll.) adopt a humble tone or manner; use
less assertive language: Germans in Samoa. Their position was
painful; they had talked big in the old days, now they had to
sing small.
talk double Dutch • talk like a Dutch uncle
talk double Dutch —be totally incomprehensible when
speaking: Oh yea, there was a guy explaining the system — in
English and people were just looking at him as if he was talking
double Dutch.
Note: 
The expression does not correlate in meaning with the
compound doubletalk—(also: doublespeak) use deliberately
imprecise, ambiguous language to disguise the actual meaning:
The group is demanding a “genuine commitment to trans -
formation” and a move away from the “tendency to double -
talk.”
talk like a Dutch uncle —speak in a harsh, unkind manner
to educate, encourage, or admonish a person: Just because he’s
older than me doesn’t give him the right to talk to me like a
Dutch uncle!
talk down to someone • talk up to someone
talk down to someone —talk in a way that suggests that the
speaker is superior: It’s unwise for a lecturer to talk down to
his audience.
talk up to someone —
1
. be obsequious or super-respectful
when talking to a person in a higher position, etc.: Don’t talk
up to someone, as if they are better than you. Don’t talk down
to someone, as if you are better than them. You are equals. 2.
talk to smb. in a friendly and persuasive manner so as to gain
favor, connections, etc.: He knew how to move at different
levels; he could talk up to people at different conventions …
he knew how to connect.
See also: chat someone up / talk someone up.