You begin to realise....
...that you're a geek, when you look up, and above you is:
a) A Newton's Cradle
b) Three copies of both the Philosopher's Stone and the Chamber of Secrets, two of the Prisoner of Azkaban and the Goblet of Fire, and one each of the other three
c) Leather-bound copies of Lord of the Rings and the Hobbit sitting next to far too many biochemistry textbooks
d) Doctor Who DVDs
e) An HMAS Hammersley cap
f) A t-shirt with a picture of the TARDIS which announces "You never forget your first Doctor".
Plus behind you is a Torchwood poster, a Doctor Who poster, two Lord of the Rings posters and two X-Files posters. You are drinking tea from a Torchwood mug and contemplating watching more of the original Star Trek.
Gotta love the feeling of mild insanity.