COL
chuckled out loud.

Let's be honest - when we say LOL, we rarely are actually Laughing out Loud.  We do, however, let out a little *a-huh-hurm*, or chuckle, once in a while, in which case you would say col.

Alternatively, you can add extra -ol's or even an -olz to the word to better explain how much you chuckled.
Jack: "...to get to the other side!!!"
Jill: "col"
Alfonzo: "COLOLOLOLZ!"