Kenny’s middle name is Bernard.
Kenny’s full name is Kenneth Bernard Watson. When he tells his mother that Byron was frozen to the car, his mother says his full name when she asks him what is going on.
“Kenneth Bernard Watson, what on earth are you talking about?” (ch 1, p. 13)
As in many cases, Kenny’s mother calls him by his complete full name when she is upset or mad at him. It is a way of signaling to him that he is annoyed. In this case, it is actually Byron she should be annoyed at. He is the one who got his lips stuck to the car mirror.