What should i wear to a bar mitzvah?

To the synagogue or to the party? Is it a party right after a morning service or is it a party at night? How old are you (13 or adult)? The answer to these questions will really help.

Wear something nice. Either a skirt or good pants if you’re a woman, or a jacket and tie if you’re a man.

Do you know anything about the denomination that the family is associated with? For example, is the service being held in an Orthodox or a Reform synagogue. Stuff like that make a different in dressing etiquette.

Why not ask your friend…?

Just dress nicely.

As @janbb said, we need to know more information of that type. Are you going to the service or the party?

Just dress formal. Same dress as you would for a wedding or other formal affair.

Wear traditional robe (robe for religion purpose).

^ A robe?

nothing! (assuming you are circumcised)

It really does depend on what part of the bar mitzvah you are talking about – you would not wear the same thing to the synagogue as you would to a fancy night time party.

@the_state_of_wisconsin
But you could offend if you’re an uncircumcised goyem.

Also, the denomination matters, particularly for women, especially if you are going to the religious service portion of the event. For example, women at Orthodox synagogues typically wear skirts (not pants) that at hang below the knee. Most (but not all) women at Conservative synagogues wear skirts rather than pants to religious services, although the skirts are often above the knee. Reform temples tend to be a little less formal and more women can be found in pants.

You can’t go too wrong if you dress similarly to what you would wear to a wedding and/or reception afterwards.

The only exception, as noted, would be for Orthodox. They are far more strict in acceptable dress for women.

I should also add—If it is an Orthodox event, you should wear a top that has sleeves, whether it be for the service or the reception. If it is a Conservative or Reform ceremony and you want to wear something sleeveless to the party portion of the event, you may want to consider wearing a cardigan, shawl, or shrug over it to cover your shoulders while you are in the synagogue for the service. I am not too familiar with codes of dress in Reform settings, but I imagine that sleeveless tops/dresses may be more acceptable there, however.

@the_state_of_wisconsin
Bitch if you’re going to edit at least note it. It makes my comment look nonsensical.

You could wear a Wonder Woman, Xena: Warrior Princess, or a Buffy Summers costume, or if you’re really feeling brazen, you can dress up as a French Maid. :-)