That Mr. Matthew Pocket is paid for his advice on "domestic economy" is humorously ironic because in his own household any suggestions that he makes in this area are completely ignored. In Chapter XXIII, for instance, Pip is invited to dinner at the home of the Pockets and while there is amazed as the child-rearing that is more of a "tumbling-up" than management. In this chapter, Pip observes that Mr. Pocket can do nothing to control the chaos of his household as children barely escape harm from falling and from nutcrackers. But, while all this goes on, Mrs. Pocket refuses any constructive suggestions from anyone. Therefore, in his frustration, Mr. Pocket puts his hands into "his disturbed hair" and appears to lift himself up by it. Then, he quietly goes on with what he has been doing.
In Chapter XXXIII, after Pip has visited Estella on Richmond Street, he draws near to the home of the Mr. Pockets and points to the irony of Mr. Pocket's being a domestic advisor,
Mr. Pocket was out lecturing; for he was a most delightful lecturer on domestic economy, and his treatises on the management of children and servants were considered the very best text-books on those themes. But Mrs. Pocket was at home, and was in a little difficulty, on account of the baby's having been accommodated with a needle-case to keep him quiet during the unaccountable absence (with a relative in the Foot Guards) of Millers. And more needles were missing than it could be regarded as quite wholesome for a patient of such tender years either to apply externally or to take as a tonic.
Then, in the same passage, Pip states,
Pocket being justly celebrated for giving most excellent practical advice, and for having a clear and sound perception of things and a highly judicious mind, I had some notion in my heart-ache of begging him to accept my confidence. But happening to look up at Mrs. Pocket as she sat reading her book of dignities after prescribing Bed as a sovereign remedy for baby, I thought—Well—No, I wouldn't.
The contrast between the reality of the Pocket home and the content of the lectures that Mr. Pocket so competently delivers is indeed sharp. Hence, the irony exists.