It's offensive in certain contexts. For example...
You have 20 years of networking experience. You've done wiring, set up hubs, switches and routers, configured TCP/IP, DHCP, NetBIOS, NetBEUI. You've done VPNs. You've set up routing tables based on star and ring topologies. You've installed wired, wireless and satellite networks. You even tweaked bang paths when using UUCP in order to save one hop.
Then one day you are asked to fix an intermittent network glitch affecting one end of the building. Days go by and you can't pin it down. All the equipment and all the wiring checks out but the network keeps hiccupping every once in a while. To minimize disruption, at night you try swapping equipment, trying different jacks, patch cables and even hubs. But the problem still comes back later.
You're in the wiring closet looking at equipment for the 20th time one day when one of the maintenance people comes by. After you tell him what you're working on. he says, "You're having problems with equipment run out of this wiring closet? That's strange, it's one of the cleanest ones in the building." Uh, cleanest? "Yeah, we've been working on this drywall on and off with the electric sander and to keep the dust under control I'm running the vacuum cleaner in here a couple times a day."
The light comes on and you realize you've found the problem. You explain it to the maintenance person, who rolls his eyes and says, "I guess it would take a noob a whole week to figure out that problem."