Not Ready for Prime Time
Some people just shouldn't be allowed out in public.
Almost every experienced developer knows one or two programmers who aren't allowed out in public. Some are so socially inept that they annoy or even anger the customers. They can undermine customer goodwill and in extreme cases get your project canceled.
One malady common among developers is excess candor. I've known a lot of developers who don't know how to filter information before presenting it to managers and customers. When asked why development followed a certain approach, they might say, "It's really a stupid strategy, but because the idiots at corporate told us we had to work with the current operations systems (which, by the way, are absolute garbage and should be completely scrapped), we have to use this ridiculous kludge to do hack together something that should be simple."
It's okay if this developer doesn't experience every stage of application development first-hand. This person may be an outstanding developer and tester, but probably shouldn't help with requirements gathering, documentation, or training. This developer should be kept away from customers and high-level management at all costs.