What are good openings to study to get more experienced players out of their comfort zone? Sometimes I end up getting the opportunity to play a friendly game with someone who has played a lot more chess than I have; these games seem more fun and interesting for everyone (and I seem to end up with a better chance of winning) when I can push play away from common positions without incurring a big early disadvantage. Are there openings that I can study to accomplish that more dependably?
You can play a surprising opening, which your more experienced opponent has probably encountered very rarely, like a gambit or a rare sideline. Theoretically-wise you will stand on more even ground then. Even better, since you will play this line often, you will have more practice with it than him, improving the odds even more. But usually such openings are seldom played for a reason, at example because they are unsound, or you have to remember very complicated lines, or they offer less winning chances than competing opening systems. There are so many such opening systems (there are even periodicals dealing exclusively with them) I don't list any of them over others.

Apart from this general thought I would suggest a more detailed approach. Try to understand what the exact nature of the advantages of your opponent (or what your own disadvantages) are and act accordingly:


Tactically much better than you?  => go for quiet lines with focus on strategic plans,
use closed systems with few tactics so you deny him the use of his
advantage
Much better theoretical opening knowledge? => use sidelines
and shaky gambits, and pray he doesn't know those ugly refutations
and critical lines
Strategically much better? => choose simple
systems and learn the ideas behind them thoroughly. You will close the
gap soon and know the resulting structures as good as he.
Generally better in every aspect? => play what you like
most and learn from your defeats


A word of warning, though. For a competing mind this might sound like a clever plan. True, it is fun to spring a surprise weapon at a stronger opponent and gain a victory this way. But, and this is a big BUT, in the long run your goal is probably to become a better player over time, and this means gaining a deeper understanding of all the chess topics. Remember you can't get better at tactics by avoiding them ;) When your opponent leaves his comfort zone, he may play weaker. But leaving your own comfort zone makes you stronger - in the long run!