I've been playing this game since late season 3 and I maybe got a penta kill once or twice, but I never felt this unparalleled surge of happiness and hype. It was more of a "ohh, I got a penta, sweet" kind of moment for me. Maybe that's just how I am, but I've seen players getting emotional when someone (often) by mistake takes the last kill and so he ends up with "just" a quadra kill, then proceeds to let that team mate know how garbage he is and how much he hates him for it. You'd think that kill steal was the equivalent of a family member dying or something, geesh.
P.S.: If I see someone about to get a penta, I just stop auto attacking or using abilities, even if that makes me lose an assist for it, because I'd rather see someone get a penta kill than one of our team mates getting flamed for the remainder of the game for stealing "his" kill.