(An incomplete and unordered list)

1. inheritance
2. !=
3. ===
4. not in  from python
5. .. and ... (flip-flop operators)
6. implicit type coercion
   1. (except arguably short -> long style)
7. null
8. case fallthroughs
9. non-exhaustive case statements
10. the switch/case construct in general
11. lambda‘s restrictions in python
12. ruby having 3 (? maybe more?) types of function objects
13. memory-location equality comparisons
    1. ok, these are sometimes fine, but should never be the default
14. arguments that can be either positional or named when called
15. anything that exposes the difference between co- and contravariance because of a type error (lookin’ at you, Java arrays)
16. constructs whose behaviour is partly controlled by the parser (e.g. php’s instanceof)
17. constructs that affect the runtime behaviour of the interpreter (e.g. php’s __halt_compiler or ruby’s __END__)
18. operator overloading where you have to (can?) define your own precedence/associativity (no, seriously)
19. compiler warnings
    1. ESPECIALLY warnings that cannot be turned into errors
20. function scoping
21. closing over variables
22. closing over values
    1. why is it never the one i want!!
23. hygienic macros
24. unhygienic macros
    1. why is it never the one i want!!
25. raw-text replacement as “macros” (e.g. the C preprocessor)