Magnum P.I.
[http://archiveofourown.org/works/830619] - - public:opalsong
Stiles is in an imminent sexual situation and, being the awkward virgin that he is, has no idea how to go about getting condoms or what size to get. Rather than asking Scott, he calls Danny. Because you don't talk to your best friend about what your penis is up to or who it's going to be in. And Danny's smart, right? Good plan?