I do not actually recommend wearing a sleeveless hoodie to any formal occasions. Sleeveless hoodies are considered very casual attire and would generally be inappropriate for most formal settings.
Formal occasions where a sleeveless hoodie would not be suitable include:
- Wedding ceremonies and receptions
- Black-tie events
- Formal dinners, galas, or fundraisers
- Business meetings, conferences, or corporate events
- Job interviews
- Graduation ceremonies
- Religious ceremonies like weddings, funerals, etc.
The key characteristics of formal occasions are that they typically require more dressed-up, conservative, and traditionally appropriate attire. A sleeveless hoodie, even a higher-end or fashionable one, would be too casual and out of place.
For formal events, the expected attire is usually suits, tuxedos, cocktail dresses, evening gowns, and other formal wear options. Anything too casual like a sleeveless hoodie would be seen as disrespectful to the occasion and the other attendees.
There may be some very rare exceptions at very relaxed or creative formal events, but in general, a sleeveless hoodie should be reserved for casual, everyday wear and not formal occasions. The best policy is to err on the side of being overdressed rather than underdressed for formal events.