This is way too simple for a instructable!
The main idea is to keep you coffee or tea warm at the office, there are many devices that use USB power to do that... but your computer already generates heat so... and mine is a i7, they get hot easily.
I grabbed a old pentium heatsink and put it in front of my laptop heat fan, it gets incredibly hot!
I keep my laptop elevated from the desk so in this case i had to improvise some legs with a clip, to keep it just in front of the vents.
I keep it there always, so when I go for another cup of coffee it is already hot :-) it's been my companion for almost two years, especially in the winter.
If you use a bigger cup or a mug, try to get a bigger heatsink, and it gets even hotter if you put it with a slight angle.
Enjoy your coffee! or whatever keeps you awake :-)