As long as you don't wear tank tops and swimwear..you are good to go.
We booked at the last minute for Flying Fish one night. We were standing out front and wanted to get a great meal before heading back to the resort. FF was opening in approx 20 minutes. We called, got a reservation, then the girl went into the dress code. I said, ok, forget it, cancel that, we are coming from EPCOT and are in park attire. She said, oh, that is no problem, just go and enjoy. We learned from then on, park attire is fine.
This is something DL has learned long ago. I don't know why WDW keeps pushing this whole dress code thing, because it is suggested, not required and we no longer pack extra close for signature meals.
We even overheard the hostess at AP one time when a couple asked if they could dine in their shorts, say yes, of course you can, we don't know why disney dining keeps saying otherwise,lol.
These days with flight restrictions and baggage charges you think WDW would just be happy someone was actually eating in their restaurants so they can keep people employed.