Had this happen a few times but every time the zip was broken on my bag.
Asok - two guys walked near me, one on each side, and I felt my bag moving so I turned and looked. I just saw his hand on it then one guy walked off into the dark soi and another walked past quickly.
Chitlom - a young girl was walking really close behind me. I stopped to look at my phone and she bumped into me and then just stood there.
Beach place cafe area - We had a picnic and walked a few metres to take a photo. When we got back picnic has gone. They took all the fried chicken and left the rice. Which is funny because the way it was packed they would have to take out the rice first in that order so not a stray dog.
Lucky for me I laced it with poison.