if it's a recurring issue, or there are little trains of foragers tracking round the zone harvesting and screaming at each other in ooc... i go to a different area if the zone is big enough, a different instance if available, or a different zone altogether. of course, if someone runs up to forage a node i'm working on, i'll /sigh or /say ... , but only to give him/her a chance to look at what s/he just did.
the best part is... many of the people that i've had do this to me have been after a particular type of node... and if i'm in a small space, i just let them go and stop harvesting. sooner or later, they'll run out of that type of node, and leave, and, at that point, i'll go fishing. it's worked several times :).
i don't mind if someone's been courteous and harvests in the same area i do, and i usually will let that person have a node we've both seen. as a matter of fact, if someone is standing next to a node, fighting or no, i wait to see what that person does with it. if s/he moves on, i harvest it. if that person harvests it, it'll respawn something else anyway :). i only become irritated if people are being inconsiderate, at which point i move on.
in the end, yes, having to forage and not getting the items you are after can be frustrating, but it's not worth getting upset over. if someone's being a hinderpart, in any regard, i remind myself that there's enough space, and enough to do, so that if i get frustrated with one aspect of the game, i can take a break and go do something else. this goes for grouping, too :).
and then there are the alts ... :D. if i'm *really* frustrated... i go roleplay the troll scout, who is rather naïve and will be moving to qeynos as a result of teen angst so that he can sing happy songs when he grows up to be a troubadour. he gets shiny object syndrome a lot, so he goes from harvesting to killing those mean goblins in the blink of an eye :).
y'all have a nice day!
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EQ: Runyaessz, 5 Monk, Phinigel
EVE: Runym/Runyn/Runyl, 43M SP each
SWTOR: Pardoric, 22 Merc, on vaca
EQ: Runyariel Varyuvantel, 65 Enchanter, Tarew Marr, on vaca
LoTRO: Runyarian, 38 hunter, Vilya, on vaca
WoW: Runyarian, 70 hunter, Muradin, on sabbatical
EQ2: Runylala, 25 Troll Bard, Qey, Blackburrow, retired
WAR: Runyael, 30 DiscO Khaine, Ironfist,retired.
CoH: Hissing Chicken, 16 Scrapper, Pinnacle, retired