In plain words
Self-glorifying, stubborn, filled with the pride and intoxication that wealth breeds, they perform yajñas in name only, hypocritically and contrary to proper rule.
Word for word
Self-esteemed, unbending, possessed of the pride and intoxication of wealth, they sacrifice with yajñas in name [only], with pretence, against the injunctions.
आत्मसम्भाविताः स्तब्धा धनमानमदान्विताःयजन्ते नामयज्ञैस्ते दम्भेनाविधिपूर्वकम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
आत्मसम्भाविताः सर्वगुणविशिष्टतया आत्मनैव सम्भाविताः आत्मसम्भाविताः, न साधुभिः । स्तब्धाः अप्रणतात्मानः । धनमानमदान्विताः धननिमित्तः मानः मदश्च, ताभ्यां धनमानमदाभ्याम् अन्विताः । यजन्ते नामयज्ञैः नाममात्रैः यज्ञैः ते दम्भेन धर्मध्वजितया अविधिपूर्वकं विधिविहिताङ्गेतिकर्तव्यतारहितम् ॥ १७ ॥
In plain words
'Self-important' -- because they've decided, all on their own, that they're distinguished by every fine quality there is; esteemed by themselves, certainly not by anyone genuinely good. 'Stiff-necked' -- inwardly, they bow to no one. 'Puffed up with the pride and arrogance that wealth brings' -- endowed, that is, with both: the pride and the arrogance money buys. They do perform sacrifices -- but sacrifices in name only -- driven by sheer hypocrisy, flying the banner of righteousness with nothing behind it, done the wrong way, missing every element and procedure the rules actually require.
Close to the Sanskrit
'Self-conceited' -- through supposing themselves distinguished by every good quality, esteemed by themselves alone -- 'self-conceited' -- not by the virtuous. 'Stubborn' -- of unbowed spirit. 'Endowed with the pride and arrogance of wealth' -- pride caused by wealth, and arrogance -- endowed with those two, wealth-pride and wealth-arrogance. They perform sacrifice -- with name-only sacrifices, sacrifices in mere name -- they, out of hypocrisy, through the mere display of righteousness, contrary to prescribed procedure, [that is] devoid of the ritual elements and procedures enjoined by rule.