It works like this: You buy these t-shirts in pairs, and when you're away from the owner of your paid t-shirts your lit up heart level languishes at two and a half. Come within hugging distance though, and you rocket right up to six.
Riiiight. I can think of no more alienating way to demonstrate a) you're taken b) you're a massive geek and c) you're desperate for everyone to know you're taken and you're a massive geek. If you're even considering purchasing these shirts, you step away from the computer and go and get some air. Alone.
However, if you're determined to get one anyway, you can get yours from ThinkGeek here.