:barbosza!barbosza@barbosza.tmi.twitch.tv PRIVMSG #pggamesbr :My text
I want the part after the second ':', but i can't split by ':' because sometimes contains it too.
You can split and specify the maximum number of items, so that everything after the second colon ends up in the third item:
string[] parts = str.Split(new char[]{':'}, 3);
The part after the second colon is now in parts[2]
.