One glass inside another

Surely hot water would break the glass?

gently tap them

You couldn't fill the outer glass as the inner one would get in the way of the filling! Just stand the 2 in hot water to expand the outer one, ice or cold water in the inner would help too.

Don't have the water too hot.
Some washing up liquid in the water helps

ooh i remember trying to part them and the one outside shattered ouch

crazyH

Stand them in a bowl of hot water. The outside glass will expand slightly and you will able to separate them. Good luck!

Yes.
Don't fill the inner one! 😀

They may break, of course.
Best not to put one glass inside the other in the first place.

I sometimes struggle to free the top of a new bottle of squash. I cut through the little plastic lugs to separate the cap then run it under a hot tap, after which it easily opens.

WD40.

Just joking!

If we haven't used a glass decanter in a while (!) the stopper is often stuck. I just pour a little water around it and it come free. Not quite the same but its sparked a hint in me.

Put ice in the top glass and stand the two in a basin of hot (not boiling) water. The ice will contract the top glass and the hot water will expand the bottom one.

Stand them in a bowl of hot water. The outside glass will expand slightly and you will able to separate them. Good luck!

I would think the slightly bigger of the two. Based on my very rocky science knowledge, heat expands, so the slightly bigger glass should expand enough to free the smaller one. But that may not be accurate!