This was a pretty interesting buggy scenario I found while reading the clang-tidy checks. If you’re writing a function that takes a forwarding reference (what looks like an rvalue reference, but whose type is a template argument), you need to be careful to not call std::move on it. You need to make sure to call std::forward instead. Otherwise, you might accidentally trigger a move on an object passed by a caller! This would be confusing, since their object would be moved from, and they never explicitly called std::move on it.
I got bit by unique_ptr when implementing a linked list today. You need to be careful to manually release() the unique_ptr before resetting or you might accidentally free the entire list. This comes up when doing insertions and stuff like that.
Filmed a screencast exploring some neat mmap behavior — read bits are not enforced for memory mappings. This is because the underlying x86 page table entries have a single bit to toggle between “Read” and “Read/Write”.