sometimes thinking of something silly, or always with a 'smart/cheeky' answer that might be naughty to someone else. off course i would not answer loudly so i laugh to myself. or i would remember something funny and laugh, annoying those around because i wouldn't share the joke.
Ok so I dont roll around going stop it atop it, but I tickle myself all the time. In fact very few peole can tickle me as well as I tickle myself. I tickle my arms in my sleep, I also like tickling my tummy and sides.