S. R. Faruqi:

The theme of the opening-verse is fresh-- that the flower has become somewhat arrogant, and has somewhat adopted a style like that of the beloved. But the verse is to a large extent unsuccessful, because for the flower's becoming arrogant, or its adopting the beloved's style, no 'proof' [dalīl] has been given. It seems that a new theme is successful when it would have been established by a (poetic) proof, or else when it would be a kind of theme that would have no need of proof.

The meaning of dimāġh meñ bū jānā is 'to create arrogance, to become arrogant'. The original saying is dimāġh meñ bū , and it can be used with jānā , honā , pānā , etc., as these verses show. Sauda:

magar vuh dīd ko āyā thā bāġh meñ gul ke
kih bū kuchh aur maiñ pāʾī dimāġh meñ gul ke

[perhaps she came to look at the rose-garden
for I found the scent somewhat more, in the head/nose of the rose]

Qa'im Chandpuri:

jo bū kuchh aur bharī ho dimāġh meñ gul ke
kahūñ kih vuh abhī latte le bāġh meñ gul ke

[if some other scent [i.e., arrogance] would fill the head/nose of the rose
I would say that she just now would scold/reprove/'take a stick to' the rose-garden]

By way of commentary I would maintain that among these three verses, Sauda's opening-verse is the best, because its theme is proved. In Qa'im's opening-verse too the theme is complete, but in his case the 'flowingness' is less than that of Mir and Sauda.

The idiom dimāġh meñ bū meaning 'arrogant', or only bū meaning 'arrogant', does not exist in Persian. It is not found in Urdu dictionaries either. Farid Ahmad Barkati, relying on Asi, has written that it means that 'the rose has become somewhat arrogant'. What greater proof of the deficiency of our dictionaries can there be, than that even an idiom used by three famous eighteenth-century poets is ignored by them? [A discussion of the errors of several Urdu dictionaries with regard to variant forms of this idiom.]

Though nūr ul-luġhāt gives a correct meaning, 'for there to be agitation/ardor [dhun]'. As evidence for this meaning, it also gives a verse by Amir Mina'i:

bū-e yūsuf miṣr se kanʿāñ meñ lāʾī hai ṣabā
ab dimāġh-e ḥaẓrat-e yaʿqūb meñ bū aur hai

[the scent of Yusuf, the breeze has brought from Egypt to Canaan
now in the head/nose of Hazrat Yaqub, the scent/agitation is more]

It's a proof of the simplicity of the compiler of the nūr ul-luġhāt , that he noted dimāġh meñ aur bū honā as a separate idiom, and gave as a meaning for it 'for there to be some more agitation in the head', and has given as a 'warrant' this verse of Amir Mina'i's. Although it's entirely clear that the word aur is not a part of the idiom.

Mus'hafi has used dimāġh meñ bū pahuñchnā in this same sense (for agitation to increase):

nah baiṭh sāʾe tale jā ke bāġh meñ gul ke
mubādā bū tirī pahuñche dimāġh meñ gul ke

[don't go and sit in the shade of the rose-garden
God forbid that your 'scent/agitation would arrive in the head' of the rose!]

Now it has also become clear that just as with dhun people use samānā , honā , pahuñchnā , etc., similarly with dimāġh meñ bū (meaning 'agitation/ardor') they use samānā , honā , pahuñchnā , etc. It's clear that dimāġh meñ bū also means 'arrogance', in addition to 'agitation/ardor'.

A final point is that since dimāġh means 'arrogance', and also 'nose', between dimāġh and bū there are layers of wordplay upon wordplay.

FWP:

SETS
MOTIFS
NAMES
TERMS == IDIOM; PROOF

I'm glad that at the last minute SRF got around to mentioning the double meaning of dimāġh as both 'mind, head' and 'nose' (see the definition above), because it's really the chief charm of the verse, since it provides those layers of 'wordplay upon wordplay'.

I know that 'gone to the head of' isn't a perfect counterpart phrase, but at least it conveys the sense that there's an idiom there, and a nice multivalent one too, for us to relish. Other than the idiom, after all, there's nothing much to notice about the verse except what SRF rightly calls its unsuccessfulness.