The hardest thing about commenting on the Internet is knowing when to totally lose your shit. Don't fly too high too fast. Pace yourself.
Say your uncle posts his daily "Benghazi Cover-Up / Obama Lies!" update. You can't compare him to Hitler right off the bat. Give him a soft ball about Rush, then work the "Jesus wouldn't be Republican" angle.
As the high taxes vs low taxes, family values vs gays stuff heats up, bring in the oil industry endangering our children (and don't forget to warm up the CAPS LOCK key).
Once you reach Defcon 2, you take abortion or gay rights out of the holster, equate his beliefs with those beliefs that lead to the rise of Hitler, and watch those capitalized letters and abbreviations fly.
By Defcon 1, beat that CAPS LOCK like it owes you money. And for content, let them know that they don't have a "FUCKING LIFE!!!!!" The evidence is in the fact that all they do is comment on the Internet (you're not guilty of this yourself since you're on the internet in defense of all that is right and holy). A snarky "#LOSER!!!" is just what the doctor ordered to wrap up the discussion.
Don't worry about misspellings, this is honest, political discourse (what America was founded on), a topic far too lofty to worry about details like letter placement.
Remember that practice makes perfect. After a few weeks, your Facebook page will read like a modern-day transcription of the Lincoln-Douglas debates.