I usually get
“look at the tyres on that!”
or, from other cyclists:
“they must drag…”
Once, on a climb I got:
“Ha ha, I bet those wheels feel heavy…”
When we got to the top together it was followed by:
“Well, I guess it climbs so well because it has a rigid fork…” 8)
I was in the middle of a conversation with a photographer setting up to take a landscape picture when I was out on a ride. He abruptly broke off and drifted into silence. He came back to life and said “Sorry, I just noticed the size of the tyres on your bike”.
Fat bikes: for attention-seekers everywhere 😉