The best way to deal with these types is Socratic questioning. When they make a dubious claim, you continually ask "why?" until you uncover the leaps of logic t

The best way to deal with these types is Socratic questioning. When they make a dubious claim, you continually ask "why?" until you uncover the leaps of logic that they've made without backing evidence. This worked extremely well on a coworker who genuinely was a nice guy and meant well, but was prone to making these unfounded assumptions. He was the type that would get a production error report and rather than calmly follow the stacktrace, would jump to a guess as to what triggered it. Simply by saying "why do you think X caused the error?" and suggesting "why couldn't it be <other part of system mentioned in stacktrace> causing it?" would force him to confront the evidence and rethink his process. Sadly he also had a habit of blustering on higher-level things to management, which eventually caught up to him when risky guesses didn't pan out enough times and management labeled him as a bullshitter.