When the enemy team gets first blood and a teammate says "GG"

Yeah... it's a difficult thing when teammates tilt like that. The hard thing is responding in a way that doesn't tilt them further or make them think that you are optimistic to a dangerous level :P

but giving first blood is weakness?

What if the person giving away first blood is a Tryndamere?

"And weak Senju disgust me even more"

edgy

and then you lost the game, with the FB giver being 1-10 and afk.