Assalamualaikum, i would like to know if it is haram for a guy to wear a hairband that a girl gave him on his wrist

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If you mean by the hairband, the band that women use to tie and fix their hair, then the basic principle on wearing it on the wrist is that it is permissible. However, if wearing it on your wrist is an imitation of the immoral people or non-Muslims, then it is forbidden for the reason of imitation. A Hadith reads: “He who imitates any people (in their actions) is considered to be one of them.” [Abu Dawood and Ibn Hibban graded it as Sahih (authentic). The same thing applies to a man who puts it in his hand as a reminder of the forbidden love relationship between him and a woman who is a non-Mahram to him.

Whoever loves a woman, let him propose to her from her family, and not put a band on his wrist that reminds him of her and arouses his longing for her, because this is a cause for more temptation and attachment to her, and it may lead him to fall into a forbidden relationship with her, such as being alone with her, or something greater than that.

We advise our Muslim brothers to fear Allah The Almighty and to avoid establishing forbidden relationships between non-Mahram men and women on the grounds of love or friendship.

These kinds of relationships are nothing but one of the steps of the devil by which he drags the person to fall into fornication or adultery.

Allah knows best.