The skit began with Lester introducing himself and explaining why he was wearing several visible bandages (including the usually cartoon-unique criss-cross of Band-aids -- ever see that in real life?) However, he was a glutton for punishment because he was about to engage in the exact same activities that caused his injuries from before.
First he sees a book or box of matches on the wall. He says "Hmmm, I think I'll play with them." At that point his friends (3 or 4 AMs, male and female) appear and say in unison, "Les-ter, keep away from those matches or we won't be your friends." Lester immediately complies and stands "away" from them.
Next he encounters a bunch of broken glass shards on the wall. "Hmmm, I think I can build something with them." The friends repeat their appearance, this time admonishing him to steer clear of the broken glass.
There was a third caution but I forgot what it was.
At the end, the Lester meets his friends and he announces that he will stay away from each of the aforementioned dangerous items. He added "...but I'm gonna stay close to my friends!" They all cheer.