The very reason you say something like foo is to avoid using any specific example that might actually mean something and confuse the listener into thinking it matters and focussing on some irrelevant detail instead of the actual concept being illustrated.

You detest that someone says "thing" instead of "house" or something?

"...so you take a thing-"

"what thing?"

"It doesn't matter. It might be anything. So you-"

"A car?"

Come on man.