For example, I watched him a few times trying to sell his product to a customer based on the high level buzzwords, but when the conversation starts getting technical because the customer is trying to understand how their product might help solve a particular problem, he'll say things like "let's take a step back from the solutions and let me understand the problem you're trying to solve", even if the customer at that point really does want to talk about the detail.
Or, after I explain a particular customer's situation, he'll ask me "why don't they use [product X]" which is an irrelevant fit for the problem. I've had more productive conversations talking directly with Sam's engineers, and I've heard from some of them that they feel he's adding negative value due to his lack of technical depth.
Now my manager is asking me to work closer with Sam on a project, and I find it difficult because I feel like he's dragging conversations backwards or derailing them due to lack of technical understanding. Moreover, Sam projects very high confidence, and doesn't look aware of his deficiencies.
How would you deal with this? I'm thinking of telling my boss what I think about Sam and ask to be left alone, but part of me feels shitty about badmouthing Sam.
The extra challenge is, I sort of lied: Sam is actually a woman, in an extremely male team (~80%, and both I and my manager are men). I just didn't want my post to sound like a misogynistic rant... It causes me extra concern because I want to help her succeed as much as possible, and in my past experience when I've provided constructive feedback to women, on a couple occasions they told me they found it sexist.
One thing to consider. I absolutely treat everyone equal, but that doesn't mean I approach everyone the same, or work with them the same. Even two guys of the same age might have very different styles, one being more sensitive and another used to direct feedback.
For women in tech, life isn't always easy, and many times they will feel that they need to put up a defensive front and hide weakness (some men do too). Give her the grace to assume she isn't incompetent and just needs some non-judgemental mentoring. I've found that if you talk to people genuinely, not being condescending, and just show that you recognize it can be hard they will start to drop the barrier (at least with you) because they'll realize you aren't that person and you are open to helping them.
All that said, her manager needs to know how the team feels, and in the end her gender should never be a factor in the hiring or firing decision. With some mentoring and help she either succeeds or leaves. Usually IME, if you give people mentoring and it is just past their ability they will leave on their own, even more so when they have seen the company put effort towards helping them and they just don't get it. Guilt and embarrassment kicks in for most people and they'll leave on their own at that point.