You have to become a moderator or an administrator to push-pin a topic. Or, you can request a thread be stickied (push-pinned). But in that case, the thread will have to be well-written and about a topic that is often repeated. (?)
Like invalid777 said, only AG mods and admins can decide and act on whether a thread will become a sticky.
If you have a topic that might (in your opinion) be viable to become a sticky, you should contact a moderator and ask if it can be executed. It's up to him/her to decide whether it's suitable to become one or not.
Ahm... what would the point be of having a random thread getting stickied? =/
And I'm pretty sure no mod or admin will sticky a random thread, unless it's going to be a viable topic users are going to talk about a lot... either that, or presenting a lively topic will do! Hmmm, guess that sounded a little similar there... *chinrubs*
