I really envy people who saw this in packed theaters in '81 where I can imagine the audience must have been in riotous hysteria in some of the funniest sequences. Some comedies work so much better when you're watching it with a crowd. There's Something About Mary and 40 Year Old Virgin were two examples I can think of where the audience roared with laughter for prolonged sequences.
I was there.. so was my girlfriend (now wife). My recollection was that most of the guys were laughing so hard they had trouble breathing, and the girls were looking at the guys and wondering what the hell thought was so funny.
I remember my cheekbones killing my afterwards from laughing so hard and so long, particularly the principal's office scene when they were discussing ways to identify the offending tallywhacker.
OMG! Porky's actually helped a couple fall in love! You should watch it with your wife on your anniversary! She probably gets the jokes now she might not have gotten when she was around 20!