Like most Caribbean islands, Barbados has the poisonous Manchineel Trees.
Upon contact the sap seeps into your skin, causing internal burns that result in terrible, painful blisters.
Even touching the tree bark will cause blistering. Burning will start immediately upon contact. Eating one of these apples will result in death. If you are unlucky enough to come into contact, rinse the affected immediately. All Manchineel trees in Barbados have signs posted to stay away!
I think with the Mango trees, you have to be allergic to them and many people are.