In a less heterosexual sense, a cocktease can also be a guy (or girl, but since there's cock involved...) who would like to experience some same-gendered groping or messing around, but, for some reason or another, won't reciprocate. This is understandable — really. It's only polite to respect other people's hard limits. It is also annoying as all hell.
Men can be just as oblivious as to their effect on other men, despite rather obvious physical side-effects of attraction. Unfortunately, there isn't a narrative of masculine objectification in the popular consciousness for the unsuspecting cocktease to avoid. Thus, often times they don't even know they're playing with their best buddy's libido.
Such relationships usually end in tragedy. Some people are helplessly attracted to people who don't share their orientation — this is sometimes called straight addiction.
Please, don't go calling people cockteases. It isn't nice.