This thread may already exist but I thought given humor is such a central part of sg1, I create a new one .
For me the funniest moment was an exchange between Jack and Jakob when they were on a goa'uld ship in the episode Enemies. Jakob kept saying "We're not gonna make it" but they made it. Jack confronted Jakob saying something like "maybe next time it looks like we won't make it you should wait and see". Jakob replied, "and blow the last chance I might ever have to be right?"! And Jack had the same reaction I did when I watched it: "What?!"
I hope this is on topic.