I recently came across a code which used the following method to check file extension:

if (fileName.toLower().endsWith(".xml"))

Clearly the author was not aware that the endsWith/startsWith has a second argument for the case sensitivity.

I think it would be beneficial to add a clazy warning to highlight this. 

To summarize:
Throw a warning like "use the cs argument of the endsWith/startsWith" in the case if:
There is a chained call of toLower()/toUpper().endsWith()/.startsWith()
And the endsWith() startsWith() has a single constant argument which does not contain any upper/lower case characters.

I do not know if it is achievable by the clazy (having access to the arguments, types, etc.)
If the idea has positive feedback I could look into implementing it.