Bob Newhart's return to "The Big Bang Theory" Thursday was like Professor Proton's Alka-Seltzer rocket: "Pop, pop, fizz fizz, oh, what a blastoff it is!"
Once again, Newhart — who won an Emmy for his first "Big Bang" guest gig — soared to the stratosphere of comedy with his delightfully dour portrayal of Arthur Jeffries, aka Professor Proton.
The curmudgeonly former children's TV host was crankier than ever — especially when Sheldon (fellow Emmy winner Jim Parsons), in a fit of jealousy, paraded Bill Nye the Science Guy into the lab where Jeffries was working with Leonard (Johnny Galecki).
Poor Bill Nye — playing himself after a stint on "Dancing With the Stars" — didn't stand a chance ... especially after Sheldon announced, "Sorry, I replaced you with a newer model!"
Here's a roundup of Professor Proton's best zingers:
"Ho-hold on. You have a girlfriend." — Stuttering in shock to Sheldon, after he introduced Amy (Mayim Bialik) to the "television legend" during a chance meeting at the drugstore.
"I remember your girlfriend. Is she here?' — To Leonard, looking hopefully around for Penny.
"Of course you woke me. It's 7:30." — To Sheldon, who dropped by his house after dark to apologize for being annoying.
"Sheldon, in a couple hours I have to get up, pee and then wander around the house." — Justifying his refusal to invite him in.
"If someone had told me that people would still call me Professor Proton when I was 83 years old, I never would've quit smoking." — To Leonard, his starry-eyed lab partner.
"That's what I told my lawyers." — Barking to a gushing Bill Nye, who said, "My show never would've happened without yours!"
"Haven't you stole enough from me? Back off, Bow Tie!" — When Nye expressed interest in his experiment.
"This is so exciting, I feel like I'm 75 again." — To Leonard, preparing to launch their lab test.
"Why?" — To Leonard, who explained he puts up with Sheldon because they're friends.
"You know you're describing a dog." — After Leonard praised Sheldon as being loyal, trustworthy and fun.
"He probably stole his wallet too." — Upon learning that Bill Nye ditched Sheldon at a smoothie place.
"So, do you have any single grandmothers?" — To Penny.
"Happily?" — When Penny told him both of her grandmothers were married.