Wow, you are seriously an idiot - go back to 9th grade. Do not pass Go. Do not collect $200. Look at the definition again. With me here? Ok, good. Now...you can take this a couple ways according to the definitions I provided. Both definitions work if you have half a brain.
First, "an unwholesome atmosphere." An atmosphere could definitely be a physical cloud, such as smoke, no argument about that. What about a non-physical "cloud"? Here is one (of several) ways to define the term:
Atmosphere: A particular environment or surrounding influence; 'there was an atmosphere of excitement'
Amazing, I didn't realize that excitement was physical. Yet, you can have an atmosphere of excitement! Even the definition of miasma I gave you provides for a non-physical atmosphere. So, you're wrong there.
Secondly, can confidence be a plague? Sure, in that it can have unhealthy and unwanted effects (becoming blind to your own stupidity, for example) if you wanted to compare it to a physical plague. But wait! The use of the word plague isn't limited to physical diseases. It can also mean something simple, such as "an annoyance." The way you carry your airs of confidence and arrogance (sorta like an atmosphere too, huh?) around is certainly something that I perceive to be unwholesome, vile, disgusting, and annoying - much like the physical miasma of a fetid swamp, or a plague.
You should learn how to recognize and understand metaphors before you spout off your handle telling people how dumb they are. You should also go back and learn some reading comp. So, seriously, admit it. I am vastly more intelligent than you will ever be, since you are compelled to make the comparison. Now please take your own advice and go crawl back under your bridge or whatnot. Or come back for more, if you are a glutton for punishment - it makes little difference to me.
Edit: I don't mean to imply that ALL confidence is unhealthy or wrong. In fact, confidence in and of itself isn't a bad thing at all. How you utilize that confidence, by letting it hang around your head like a dark fog clouding your judgment, for example, can lead to confidence becoming a bad thing.
Edited, Nov 15th 2007 2:41pm by Zoltarion
(2nd edit, lol@spelling)
Edited, Nov 15th 2007 2:43pm by Zoltarion