Invited to a "fun" dinner party. With a very conservative American gentleman, some dentists, and a hostess who will probably already be drunk and says she is "a bloody awful cook". All of which demands "offensive-casual".
This looks great. Even the unrelated square somehow works for me, though I'd prefer it as a loosely pointed fold, given that it is essentially a random component in this look, so why not accept that and make a feature of it instead of half-heartedly pushing it down into the pocket. The very classic shirt/tie/jacket combination gives you a little room to be crazy elsewhere if you want.
The good doctor has pretty much summed up my thoughts on this. Alternatively, a gdl-esque fold-n-stuff might work, too.
This is why I still think a pair of navy/blue pants should be in everyone's closet. While there are several other ways to go with the tie color paired with this pant/shirt/SC combination, I still think this looks good.