It wouldn't be? I disagree. Just because the Pineapple is capable of bad things doesn't mean that's all it does. I saw a question on the Information Security SE site a while back where the OP suspected someone was hiding a Pineapple, and wanted to know how to find it so they could have the person arrested.
I whip out my Pineapple in public all the time. I've got a battery it can run off of, and I'll sometimes turn it on when I'm on a city bus or in a restaurant. I connect it to a public WiFi access point, and it broadcasts a WPA2 network I can connect my devices to that adds some protections and conveniences I like to have. It routes all my traffic through a secure VPN, adds some custom DNS entries and blocks, and facilitates direct connections between my own devices (many public networks don't allow this between 2 devices on their network in my experience). Setting that all up within iOS or Android is a pain, but the Pineapple can do it with ease.
Sure, I could click a couple buttons in the web UI and start intercepting text messages and stuff (did you know some carriers send SMS messages over WiFi when they can? Without even trying to use SSL? I know!), but that doesn't mean I actually do. It's for this reason that I wouldn't make the same assumption about someone else.
To answer your question directly: What would I do? I'd probably walk over to them and say "hi." They're probably an interesting person to talk to, and I'm always interested to network with other hackers in my area.