(Bloomberg) — Anxiety? Yes. Panic? No.As the S&P 500 plunged Monday, calm reigned on the online forum of the Bogleheads, an investing group inspired by the late Vanguard Group founder Jack Bogle and famed for its cool-headed, long-term attitude toward passive index investing.“Feeling awesome! My annual bonus hits this week and goes directly into my 401k,” one contributor said in a post.Bogleheads are notoriously blase about market volatility, but a wider range of investors also seem to be carrying on, if not exactly keeping calm, and maintaining portfolio allocations. Advisers say that clients in passive investments, such as those invested […]