Robyn,
I ask myself "where did my baby go" and she's 17!!! But about your son, it's all completely normal, even at 3. They love the potty jokes and I don't believe boys ever grow out of that! As long as he doesn't share his potty habits out in public, (my son once pulled down his pants and peed on the playground. When we asked why he said he didn't have time to get to the bathroom; besides he says "I turned my back away from the people"). When the potty talk starts at home try to ignore, or quietly say "we don't talk about such personal things, or "we don't say those things..." but I'd recommend not to make a big deal out of it. He's trying to get your goat, and it is very hard not to laugh! Once my son was in the bathroom and called his dad, quite urgently, so my husbands runs in there and find Andrew feeling his testicles and was scared to death, he said "daddy, there's something in there!". One day, you'll share your stories as well, and you'll be able to laugh too! Not to worry Mama!
V. T.