I'm trying to find countries with a tight corridor to sea, so that the countries on both sides are close to each other. Bosnia's corridor is only a few km, but both sides of it are Croatia, so that doesn't count.
Israel's Red Sea corridor is about 10km wide I think, with neighbouring Egypt and Jordan being that close to each other. This is probably the closest of the ones I've looked at.
I think Iraq's connection to the Gulf (bringing Iran and Kuwait close to each other) is slightly larger, but all these "measurements" were made by on zooming on Google Maps and squinting.
Slovenia's corridor between Italy and Croatia is similar.
Armenia and Iran get within a few km of each other, with Turkey in between, here. But that is spoiled by the fact that they share an actual border on the other side of Azerbaijan's exclave to the right.
I want to finish this by mentioning Baarle-Nassau-Hertog, which doesn't qualify (it's all either Netherlands or Belgium) but it's fun.
There are also six Dutch exclaves located within the largest Belgian exclave, one within the second-largest, and an eighth within Zondereigen.