I think adjustable spanners are an abomination - use one that fits - preferably a ring or socket.
But if I have to, I use a 'BAHCO' - a well made Swedish tool.
Or if in desperation, Stillsons, or, even worse, weld a nut to the offending part.
Oxy-acetylene can be handy too.
Or cut the B*** off with an angle grinder.
These are situations where 'Grrrr!' is the only appropriate comment.
Allan