A phrase used by elementy school students and the most common way to get one of their peers to stop doing something.
Girl: Stop pulling my pigtails!
Boy: Whadda you gonna do about it, huh?
Girl: I'll tell.
*Boy runs away from girl*
by Becks Grevau March 14, 2007
Saying originating from Belmont County, OH. Used to begin a story or after something that promotes bragging rights in a rural or backwoods boondocks area. A similar saying is That's what's up.
Ex. I put a 3" lift kit and some 31's on my Chevy Tracker the other day, I'll tell you what and such.

Ex. I caught a catfish the other night. It was a big'un, I'll tell you what and such.
by ovredneck69 June 22, 2014
a smart assed response used when someone has asked 'wat the hell?'. of course this is followed by wat is actually the hell.
i.e. Gabby walks in on her sister running about her room like a mad woman.

Gabby: Gwenn, wat the hell?!?!? you look like a retard!

Gwenn: the hell? you want the hell??? i'll tell you the hell. i just ate a bucket of sugar with a shovel!

Gabby: *sigh*
by Xx moonlight xX February 16, 2011
when something is so obvious to one person that he will not even charge, for it being to sed to a companion friend or aquaintace.
tom: what do you think of tim's mam?
muthar: she's a propa slag, i'll tell you that shit for free!
tom: thanks muthar you're so genorous!
by muthar November 9, 2004
The last thing you hear before being stabbed in the chest by a 10 cm long knife in north London. Could also be in Birmingham or Glasgow. Whatever you do if you hear this sentence run away.
Bruh, I'll tell you what mate
by INeedToGoCommitDie February 15, 2023
1. An incredibly annoying way of stating that you just don't want to tell them something; might be for personal reasons. (Knowing that you cannot get younger; it therefore means one will never tell them what you are referring to.)
Caitlynn: Why won't you look at my face when we make love!?

Me: *turns away and thinks to self "ah crap, here we go again... c'mon, think of something!* ...I'll tell you when you're younger...
by The OPB: Original Purple Belt October 11, 2010
A phrase used when something can't be explained to a child
7-year-old: *catches adolescent brother watching porn* What is this?
Brother: I'll tell you when you're older.
by frabrizio March 24, 2017