When I was commuting with a laptop and other stuff, I'd have everything in a bare-bones messenger bag, with the laptop in a neoprene sleeve, and then I'd put the messenger bag into an Ortlieb rolltop pannier and mount that to a rear rack. To get it off my back and for the waterproofedness of the Ortlieb pannier, if it rained. Being in a sleeve, and an intermediate bag, made me unconcerned with bumps/shocks while riding with the laptop in a pannier.

But this was for a 5-6-mile (one-way) commute that I'd make, rain or shine. If you're talking about a shorter ride to a cafe that's also totally discretionary, then I'd just wear the laptop in a backpack or messenger bag.

If you really don't want to wear something on your body and the ride isn't especially rough, and you have your laptop in a thick sleeve and it's totally powered off, then I wouldn't worry about the danger of incidental road chatter.