Originally Posted by capnpyro
If it were me, actually I've been in this situation, and my girlfriends dad is a regular blue collar kind of guy, I'd go with jeans and a nice button up with the sleeves rolled up and tennis shoes. I'd rather be able to easily associate with him than impress him with my smart loafers and matching pants and socks. It's true it's always better to over dress, but in this case I'd rather under dress, if he's a blue collar guy he'll be thinking 'douchebag' in his head over and over if you're dressed like you're going to a job interview. My recommendation obviously changes if you're in your 30's or 40's (I'm 26).
I just asked my g/f what he wore tonight (eating at a bar) and the answer was "jeans, an old button down, and cowboy boots" EDIT: I am 20. EDIT again: But this offers two schools of thought: 1) I may be slightly overdressed, but it will come across as respectful for meeting my g/f's father. 2) As a blue collar guy, he will see me dressed nicely and think I'm a douchebag, as capn suggested.