How does Polonius's conversation with Reynaldo change our opinion of the old counselor? What verbal mannerism does Shakespeare give to Polonius that now make him appear comic?
Polonius appears much more wily than we may have given him credit for in previous scenes. Though the following quote (3.2) comes later than the Reynaldo scene you point to, it is indicative of the way the audience has come to think of Polonius: a blowhard, full of himself, an advice giver rather than a taker. Immune to his own flaws of wordiness, Polonuis cautions: "Therefore, since brevity is the soul of wit/And tediousness the limbs and outward flourishes/I will be brief: your noble son is mad."
All in all, Polonius is like the irritating uncle at a Christmas party you can't get away from. However, in the Reynaldo scene, he is portrayed as much more dangerous than he is likely to be given credit for. His non-intended comical remarks of the past are not present in 3.2. Instead, we are shown how Polonius intends to use Reynaldo as his thread in a web of deceit in order to "catch" his son, Laertes. Cunningly, he tells Reynaldo what to do:
At 'closes in the consequence,' ay, marry;
He closes thus: 'I know the gentleman;
I saw him yesterday, or t' other day,
Or then, or then; with such, or such; and, as you say,
There was a' gaming; there o'ertook in's rouse;
There falling out at tennis:' or perchance,
'I saw him enter such a house of sale,'
Videlicet, a brothel, or so forth.
See you now;
Your bait of falsehood takes this carp of truth:
And thus do we of wisdom and of reach,
With windlasses and with assays of bias,
By indirections find directions out:
So by my former lecture and advice,
Shall you my son. You have me, have you not? (2.1.61-75)