Originally Posted by
kinglobjaw
...It was the A321 and beverage service in the back has just commenced. Cart was by row 8. An elderly gentleman sitting in row 4, ...
Perhaps you meant row 5 bulkhead, as row 4 in an A321 is FC?
I think a pax in the main cabin ought to ask a FA first before using the FC bathroom; something like, "I've an URGENT need and the cart is blocking my way/I'm handicapped and can't walk so far......may I use the bathroom up front?"