I’m not Indian but henna is also a part of my culture and used when someone is getting married. We don’t get offended but usually the designs are not done well or as if it were body paint if they aren’t done by someone who is from a culture that uses henna.

it should be fine, it is great.
http://www.hennacaravan.com/hennakits.html

Henna is not only used in India. It has a history in Morocco, Mauritania, Yemen, Libya, Somalia, and Sudan. In fact most religions at one time or another used henna.

besides that, henna art is not only used in India before marriage. Henna has been used to adorn young women’s bodies as part of social and holiday celebrations since the late Bronze Age. In fact the Night of the Henna was celebrated by most groups in the areas where henna grew naturally (Jews,Muslims, Hindus, Christians and Zoroastrians). In many places in North Africa henna was applied to protect the skin from harmful rays from the sun, and applied on the bottom of the feet in places where shoes were seldom worn.

Bridal henna techniques have a distinct flair to them and if you got it done at a fund raiser it was probably just social henna work.

Your friends should not be offended because getting henna art done is not disrespectful.

I hope the history didn’t bore you too much.