First technical interview, and please note I've been interviewing for over twenty years... Was write a full asynchronous demo, using threads and with nonconcurrent dictionary to show how it's not thread safe. Then fix it. 30 mins. It was a car crash. Maybe I should have been able to do it?! I spent two hours after that setting up my old legacy example then using DI and the decorator pattern (with semaphoreSlim) to show how I would wrap the old third-party (closed) dependency. Sent them the git repo link. Got some tosh back and decided to remove myself from the process. I think what annoys me more than anything is the total disdain for the candidate. No prep, no partial code, no guidance. I don't care who you are writing code in web browser window with no auto completion or debugger is horrible. When will these firms learn?
