no joke
seriously; in earnest
Housekeeping ain't no joke. Louisa May Alcott
Life must go on, even if it's no joke... just pretend to believe in the future. Louis-Ferdinand Céline
Look, Chief-is it really necessary to kill everybody here? I don't relish it.” "Don't get chicken, son,” admonished Ardmore with an edge in his voice. "This is war-and war is no joke. There is no such thing as a humane war. Robert A. Heinlein
To me, music is no joke and it's not for sale. Ian MacKaye
I have an airplane hangar with 17 cars in it. That's no joke. I have a 'half pipe' in there, too - you know, like a big ramp, where I skateboard. It's awesome. It's the ultimate fantasy. Paul Walker
Cease your jests, there is no joke in being ill-natured. Latin Proverb