After a sentence, either sarcastic or serious when people have started laughing, use 'No seriously' to either show

A) You're serious and want them to stop laughing because it's not funny
or
B) You're taking the piss out of them by not being serious
Amy "Hey Ashlee, do you want to come with me and my extended family to woop woop for a month or two? It'll be super fun!"
Ashlee (laughs) "Yeah, a month or two in woop woop with your extended family will be super fun!"
Amy (pissed off) "No, seriously. I think I'll go ask Sarah. (under her breath) Bitch."

Jim "Dude, last night I had a totally rippin' threesome with Carmen Electra and Jessica Simpson!"
Joe (laughs) "Like fuck you did"
Jim (laughs) "No, seriously. I jacked off alone to Judge Judy."
Joe (disgusted) "Oh, dude" (leaves)
by Kateus December 29, 2005
Get a No, seriously mug for your Uncle Bob.
Used to back up a statement that is strongly true.
Person A: Dude, the performance of Berlioz's "Symphonie Fantastique" was the best thing ever!!

Person B: For seriously!
by Sho Fo-Sho March 09, 2009
Get a For seriously mug for your brother-in-law Paul.
When she spoke to the crowd, her tone was one of seriousness.

His face showed intensity and seriousness as he strove to define "seriousness."
by Bill Foecke October 09, 2003
Get the seriousness neck gaiter and mug.
asking a question, slang word for emotion thats serious
jason: "she broke up with me and she wasn't even kidding, she was seriousing"
alex: "dude are you seriousing me? you guys went out for 3 years!"
by aakasd420 October 20, 2010
Get a seriousing mug for your dog Callisto.
This term is usually used after saying a non-intended humorous quote or phrase.

This term can also be used to put a serious twist on your joke, and frequently intensifies the situation.

It is also used to make a joke more humorous, this is called backing-up(usually used after your not-so-funny-joke)
#1:
Person 1: Yeh i got a vest the other day!
Group: HaHahahAhAh
Person 1: but seriously

#2:
Person 1: I've got a vest....jokes....but seriously
Group: HaHahahAhAh

#3:
Person 1: Vest are only for 'homos'
Group: *cough*
Person 1: but seriously!
Group: HaHahahAhAh
Get the but seriously neck gaiter and mug.