You seem to go from asking how often someone uses C4 to asking for C4 stories.  I can answer the first one.  I have never used C4...ever since I got my first throwing knife kill cam it's throwing knife all the way.  Quiet, reusable, and just plain fun.

I use C4 and Bouncing Betty all the time. Here's a video of some of my techniques for getting lots of easy kills:

it all depends on what game type and map im playing like if im playing team defender or dropzone on dome then the c4 is definitely coming out to play

How often?  Every single match, it's all I ever use in the lethal slot.  It's the best option by far.

Stories?  My best is a quad-kill on Hardhat in Dom.  I also sometimes get into showdowns with people, run around the corner and toss some C4.  When they give chase, *BOOM*.  I've gotten good at hiding satchels by objectives so alert enemies or those using SitRep can't easily see them.  A lot of times when I come upon a prone camping sniper, I'll just drop a satch on his rear end for grins >:)

776 C4 kills since 9th Prestige, that was the first time I used it.  Now I'm 15th.

I loooove it.  774 and mostly been playing S&D since 9th.

Never used it in previous CoD's, been playing since CoD4.

Got a nice triple the other day in S&D with it. 

A multi kill is 4 or more enemies. You are a big liar or just confused. 300 multi kills with C4 and 1500 total C4 kills. 300 times 4 equals 1200. That means 80 percent of the time you throw C4 you kill 4 or more enemies. I am ranked 14 in the world with C4. I have 16,000 C4 kills and around 15 to 20 multi kills (4 or more enemies) with C4. I use C4 on every class every game. You may have 300 double kills with C4 but that would mean you get a double kill 40 percent of the time with C4. I doubt it. There are a handful of people better than me with C4 and I promise you we don't get 40 percent double kills with C4. How do you know you have 300 double kills with C4. Do you write each of them down?

I use it enough to have earned the most c4 kills accolade 907 times. 3300 plus c4 kills at the moment, my favorite lethal choice by far

Here are a few of my better c4 moments.

i use c4 all the time. by far my favorite piece of equipment, and definitely the most reliable. i rarely ever get hitmarkers with it, which is awesome. Favorite places to probably use it would be on enemies taking the B flags in domination. Favorite maps would probably be carbon (throwing it from B over the wall down to A), mission (all over the place), and lockdown (on the truck next to the C flag for that unsuspecting victim attempting to sneak over to the flag.

I also have a ridiculous amount of multikills with it lol. Plus it comes in handy when people decide they want to camp corners/rooms. One good toss and thats the end of their little party hahaha the rage messages/responses are priceless.

If it isn't a Throwing knife on my class, then it's the C4

Has been hundreds of times more reliable than the frags, and semtex.

i used to always use semtex but i felt as though i was wasting them more than killing with them so i decided to try out c4 and it took me a bit to get used to but it has definately saved my life a few times...i would have to say the best c4 story i have was just the other day i was playing search on seatown and three riot shielders were camping in a corner with a trophy system, i went and threw my c4 which ended up setting off one of the RS's explosive and killed all three for the game winning kill...it was epic

A lot

I have used it 7400 times with around 1200 kills.

It was my 1st prestige token unlock.

I typically will use it in domination to "guard" a flag while the rest of our team takes a different one.  Easiest kill in the game, "Enemy taking ___", oh no they aren't.

I couldn't tell you how many multies I have had with it, but I did have a 5+ the other night in infection (dumb enemies).  I think that is my best, I don't particularly pay attention to things like this.

Boom goes the dynamite!!!