I think my favorite idea is the Bonsai simulator. Low energy investment, but you end up with something neat over a long period of time. You friends would probably think it's neat when you post an update every year. And, you don't need any new technology, someone could just make this tonight.
I found this idea particularly hilarious for some reason:
ceiling-mounted infrared beam emitters+guidance infrared camera, steered by segmenting CNN: it automatically detects & warms up the bare skin segments of female objects until thermal equilibrium of 37.5°C is reached, ensuring thermal comfort of women without requiring heavy clothing—thereby resolving the Great Office Thermostat Wars once and for all.