Yesterday was Friday the 13th, so here is a list of my worst dev nightmares without order of significance:

1) Dealing with multithreaded code, especially on Android

2) Javascript callback hell

3) Dependency hell, especially in Python

4) Segfaults

5) Memory Leaks

6) git conflicts

7) Crazy regexes and string manipulations

8) css. Fuck css.

9) not knowing jack shit about something but expected by others to
produce a result with it.

10) 3+ hours of debugging with no success

Post yours