A table is nearly always better than a dumb pie chart; the only worse design than a pie chart is several of them […] pie charts should never be used.
Edward Tufte in the Visual Display of Quantitative Information
Stop using pie charts, they are evil!
title of Bernard Marr’s LinkedIn post
I hate pie charts. I mean, really hate them.
Cole Nussbaumer in death to pie charts
Many people have criticized the pie chart. The most important critique is that we, humans, are good in comparing lengths and heights, but angles and areas not so much. The following three charts by Kristin Henry demonstrate the phenomenon. Can you spot how the two pie charts below are different?
And how about now?
OK, I admit that the order of the categories matters quite a lot in the chart above. But alternatively, you can transform the pie charts into grouped bar charts, that will immediately show the difference: 
In general, pie charts should be avoided when a large number of items is considered. Simple pie charts displaying 2-3 categories or one category as opposed to the others may work just fine, but when displaying more data, it is better to choose a different chart type. Oracle hosted a different example some years back:
Fortunately, there is some constructive criticism as well. Cole Nussbaumer of storytellingwithdata.com provides some good alternatives to pie charts and David Robinson of VarianceExplained.org does provides alternative charts specifically in R. Datawrapper.de discusses when pie charts may come in handy and when they should definately not be used. Finally, the below GIF funnily shows the steps in which pie charts can be improved:
Pie charts have been used for jokes before, arguably their only good purpose:
On a final note, there do seem to be even worse visualizations of data than pie charts:
paulvanderlaken.com 