A Virginia man accused of posting a threat on Facebook to detonate pipe bombs on the Washington, D.C., subway system was ordered to undergo a mental evaluation. Awais Younis, a native of Afghanistan who lives in Arlington, described to a friend how he could build a pipe bomb with specific types of shrapnel to cause maximum damage on the Metro system, according to a sworn statement from an FBI agent. When the friend suggested he was not serious, Younis responded, “Watch me.”