Very few comic book characters are completely invulnerable. You'll often hear people saying things like "Superman can't be beaten by anything other than Kryptonite" - but that's utter nonsense. The Man of Steel is vulnerable to magic, telepathy and can be defeated - or even outright killed - by a good old-fashioned beat-down if the character dishing it out is strong enough.
The thing is, they're all acceptable weaknesses and vulnerabilities - brute force, mind attacks, magical powers and a very specific form of radiation make sense as things that could harm you - but not all weaknesses in comics are quite so tenable. Some characters - many of whom are incredibly powerful and appear as though it would take something wielding magnificent power to defeat them - can be beaten by the simplest, stupidest and most mundane of objects, materials and concepts.
In many cases, you just have to sit back and Marvel at just how crazy some of these weaknesses were.
This article will list several weaknesses of a similar nature which reduce otherwise extremely powerful characters to laughing stocks. Here are ten utterly ridiculous comic book weaknesses...