I dunno, I'm sort of underwhelmed.

• use the smallest data type you need for a given purpose (which you don't really need to worry about on modern hardware for integer types)
• use bitwise arithmetic when possible
• use fake pathfinding when possible (in this case random walk), and when not possible, limit search depth
• don't do collision detection on thousands of guests; allow them to phase through each other

This is all fairly basic stuff I would hope any game dev would be aware of.