The oblivious bit? Or the crazy stalker bit?

INTPs are in their heads most of the time and oblivious to just about everything in their environment, unless it is a focus of study, in which case it is scrutinized to excess.
They are taught to believe that they are inferior in the sphere of interpersonal relations - socially maladjusted, geeky, clumsy, awkward - and tend to devalue themselves, so frequently are skeptical that anyone could really be interested in them. Beyond that, even if they are awesome and know it, few people understand them or get to see anything other than the default vacant expression / blank stare, so they believe it unlikely that they'd attract interest, or if they do, it's for the "wrong" reasons. The ability to reinterpret the same data in 1001 different ways, coupled with an aversion for premature conclusions, means that they tend to err on the side of caution when assessing other's motives. And the drive for objectivity and need for self-sufficiency mean they are less likely to project their own desires onto the object of their desires.
I've been smacked on the head with a marriage proposal before having any idea that someone was into me, but I am pretty damned oblivious, even for an INTP.