Originally Posted by imatlas
I don't think that an accurate recommendation can be made without some additional context. It's important to understand that Judaism, especially in the United States, is not a monolithic structure. In fact, there are distinct sects, each of which has developed it's own set of traditions and traditional attire for bar and bat mitzvahs (let's not forget the girls!). Here, then, is a guide to proper attire, relative to each Jewish community:
Haredi / Ultra-Orthodox: black suit, black shoes, white shirt, tassles dangling at the waist (aka tzitzit
Hasidic or Lubavitch: pretty much whatever the fashionably attired gent wore in Krakow circa 1780, as long as it's black. Bonus points if your suit smells like it has never been dry cleaned.
Modern Orthodox: as CBD as CBD comes. Dark grey sack suit, white shirt, dark tie, black belt and shoes.
Conservative: similar to MO, but blazers or muted sports coats are permissible. "Fun" ties are acceptable, as are ties with little stars of david or chai
Reform: a much wider range of suits, sportcoats and trousers are allowed, while staying within the realm of tailored menswear. Think Episcopalian wedding attire.
Reconstructionist: similar in appearance to Reform, but with obsessive avoidance of fabrics made from a blend of materials. No Cashco for you!
Humanistic: your cleanest jeans and t-shirt, preferably one that says Peace Now! in Hebrew, with Israeli and Palestinian flags on the back.
Aquarian Minyan (this may be a Berkeley only thing): just go with what feels right, dude, it's all good!