Keep in mind, being overdressed leaves a better impression than being underdressed.  When in doubt, don't wear jeans, especially to these occasions...

• A job interview or conference- Unless you've been told to wear jeans, I recommend wearing slacks or a suit, or if you're interviewing somewhere with a casual dress code you could even wear another casual pant that isn't denim, like corduroy or chinos.  Also, wearing a polo shirt and jeans does not equal weekend business wear.    
• A dinner party- Wearing jeans communicates little respect for the person who has invited you into their home.  If it is a very formal dinner party, that information should be stated on the invitation.  If you know this is a casual occasion, this is another chance to wear a nicer pant.  I love seeing a guy pull off a nice mustard or olive pant in the summer and autumn months, they're still casual and comfortable but look like you put a little extra effort in your outfit.
• Hiking or camping- Normally I wouldn't recommend cargo pants instead of jeans but if you're going to be hiking or camping, you really need to wear appropriate clothing.  Jeans are inappropriate because they do not insulate your body for cooler temperatures, and they don't breathe enough for warmer temperatures.  Wearing jeans also risks all sorts of chafing, so avoid that altogether and invest in a decent pair of hiking pants with cargo pockets.  Keep in mind that while cargo pants are generally considered unstylish, they're very useful in the outdoors.  Good for camping, bad for streetwear.
• Funerals or religious holidays-  Whether it's a somber event or a big celebration, you shouldn't wear jeans to church or to a wake.  When your outfit is elevated, you're honoring whatever it is you're participating in and events in this category demand honor and respect.  Not to mention, you look sloppy and unprepared when you arrive underdressed to Christmas.  Generations to come will see the photos your mom/grandma/sister/aunt took at Christmas dinner and if you are the only one wearing jeans and a t shirt, that will stand out.  

Remember to keep your task in mind, if jeans will be uncomfortable, skip them.  You don't want to appear to be unprepared, and knowing what to wear to what event will help you to develop your personal style.  When you're in doubt about what you should wear to an event, text the person who invited you, or the person organizing the event.  There's no reason to be embarrassed about inquiring about the dress code, if nothing else, it will show that you cared.  In the middle of an era of casual in the US, it's great to see people putting forth the extra effort.  

I'll be posting on Manly Monday again next week!  If you have any questions or comments, please leave them down below!  I'd love to hear from you, especially if there's something you'd like me to cover for a Manly Monday.