B737-900 Ramp Personnel reported a B777-300 being guided into adjacent gate as being non-standard; resulted in winglet passing over B737 vertical stabilizer. Ground reporter also stated that contract wing walker seemed rather careless.

Narrative

I was instructed by the flight deck to disconnect the GPU and Air from the aircraft (737-900 on gate XX). Then I hear an airplane coming in diagonally to gate XY; thinking it's an A330 as usual. Instead; it was a 777-300. Normally they park that aircraft over on the XX concourse; but for some reason; the Airport Operations Department placed them next to us. Normally when we have an aircraft occupying gate XX; 777s are usually towed in regardless of the carrier. I watched the left winglet come close to our tail and go over our right vertical stabilizer. And the Contract wing walker seemed rather careless about it as well. I was expecting a collision at any second and my anxiety went up because of it. Thankfully; it didn't happen. I quickly called my Supervisor and then started taking pictures of the plane to see if they did come at a weird angle. Then the flight deck called me up to the flight deck and wanted to talk to me regarding the incident because they saw my reaction out of the window; and I told them what was going on. Then; my Supervisor arrived on the flight deck as well to elaborate further on the situation and the flight crew commended us for our actions and having a keen eye.