As Rawdeal said...
1). If you're on a PvP server, then your only recourse is to either roll on a non-PvP (PvE or RP) server or do a paid server move to one of those servers.
2). If you attacked a flagged NPC or player, your PvP Flag will wear off in 5 minutes after you exit combat with said NPC or Player
3). If you entered a PvP area, your PvP Flag will wear off 5 minutes after you exit the offending area (Enemy Capital Cities, or smaller towns that have flagged guards nearby, aggroing a guard constitutes 'attacking' one now).
4). If you typed /pvp, you must type /pvp again. Your flag will wear off in 5 minutes.
5). Taking a Flight Path automatically removes your PvP Flag (regardless of how much time was left on it), assuming you're not on a PvP server. You cannot take a Flight Taxi while in combat.
Edited, Jul 18th 2011 8:01pm by Lyrailis