Bumblebee is more than aware that the conversation isn't over. Optimus wouldn't be Optimus if he has just let this go. The reason that the smaller Autobot would rather not go through the lecture is mostly because he is already aware of the dangers Tarn represents. He wants to just slide under the radar for now.

Like that is going to happen. Bumblebee is still going to make a go of it. Later.

"Who all has volunteered? Half our numbers?"

Yeah so, Bee has to tease. If it's Optimus asking, almost everyone would volunteer.