Is there a procedure to report a buggy iOS app in the app store?
The programmatic and direct feedback channels to Apple and the developer are as follows:


Report a problem from the purchase summary in iTunes on a computer. This also is useful if you wish to ask for a refund in the case where the app was paid and doesn't function in your judgement. 
There is a general problem link in the store as well as a link to developer support. These are best for technical or minor bugs that don't ruin the app experience or if you expect it to get fixed and continue to use the app.
You can write a formal review that Apple may eventually publish detailing why you feel the app is buggy or non-confomant with design guidelines or rules.
You can rate the app in stars


Those three procedures are standard ways to provide feedback about buggy apps or problematic purchases. Deleting the app sends less formal feedback as your devices stop asking for updates to that title.