This joke plays on the word "halálom", which means "my death". "Halálom" is by chance made up of the words "hal" - "fish" and "álom" which is "dream". So "Fishdream" is the same as "My death". The joke is: "Which animal is it scary to dream of? A fish. Why? It's about my death / fishdream."
How does a retired man walk around? - By fumbling around. ("fumbling" is "botorkál" in Hungarian, which starts with "bot", meaning "stick". So "sétabotorkál" is a combination of "walking stick" and "fumbling around").
"Hajbókolás" means giving compliments to someone (like royalty), but in this form "haj" also means "hair", and "bókolás" means "paying compliments to someone". So the man is complimenting the hair.