Given that I didn’t wear a tux for my wedding, it’s hard to imagine another occasion that would rate wearing one.
Likewise.
Of course, I live in a country where a shirt with buttons is considered formal wear.
Infrequently enough that I had to look up what it is. I might have had to wear a tux once for the captain’s gala on the cruise ship at age 17.
I reckon 11-20, as I have sung in one on a number of occasions, but as I’m still quite early in my amateur singing career (and my choir usually dispenses with the jacket), I haven’t built up that many yet. Have also been to a few proms and formal events where black tie was de rigeur, if not absolutely essential. As such I do own my own (cheap) dinner suit and it has certainly paid its way compared with what the cost of hiring each time would have been.
At University, I was part of a debating society whose officers had to wear them on the formal Friday night debates. There were also a fair few formal balls etc. Occasions like that have obviously tapered off a lot since then but I’ve probably worn a tux about 100 times.
I started off feeling awkward and too formal, then learned to appreciate it. Then I found it boring. You can try to jazz it up with cummerbunds and cuff-links, but basically you’re dressed like every other guy in the room. For the few black tie events I go to nowadays, I wear the kilt. Which is actually a pain in the arse compared to trousers/shirt/jacket/tie but has the advantage of being individual.
The inverse rule of tux suavity: one guy in a tux looks like James Bond. 40 guys in tuxes look like waiters.
(Or choristers, but that’s different - it’s a genuine uniform in that case.)
Three times. Senior prom 60 years ago and each of my two sons’ weddings. I wore a suit to my own wedding and also to my daughter’s. It is unlikely I will ever do it again.
I was in choir from junior high through college, and we wore tuxes for most concerts. I got up to 30 without considering special performances around Christmas time or choir camp or the handful of dates I wore it on.
EDIT: Oh, crap. Like brad_d, I probably should have went with 50+. I neglected band concerts, which would easily give me 12 more, definitely getting me over 50 with the other things I mentioned.
I own one (it’s actually my third one) due to a wedding-reception band I was in throughout the 90s. I wear it a couple of times a year now, charity balls and holiday dances. I voted 50+; the actual number is probably >500.
6-10. Prom, a few weddings including my own first.
I should have bought one… while getting my BA in music, I also played in a brass quintet and performed all over the Bay Area. Well over 50 times over five years.
Just three, I think - for a formal dance while I was in law school, at a friend’s wedding, and when I was an extra on The Avengers. I don’t own one.
I answered 6-10 but I forgot I used to wear a tux all the time in HS choir. Correct answer is 50+
I’m invited to a “Black Tie” event every summer. About half the men are in some sort of tux, the rest, like me, are in a dark suit.
50+
The Knights of Columbus Fourth Degree Colors Corps regalia is a tuxedo, together with plumed chapeaux, cape, and sword. I own a tux and have been to hundreds of colors corps events.
I own one. For formal dinner events.
Anecdote - back in High School, my crew wore them to school one day as “models” to hand out flyers for the tux shop in advance of prom. I had white tie and tails. 
6-10 but it might just sneak over 10. Used to own my own and went to all sorts of balls in the Upper Sixth and at University. Haven’t worn one in years though. Last time I had the opportunity was last Christmas, work had a Great Gatsby-themed party, but I went in the more relaxed attire of Tobey Maguire’s character in the Luhrmann film.
I can, however, happily tie a bowtie.
Zero. But I do have one of those tuxedo t-shirts.
I answered 6-10, but then I actually counted and it was closer to fifteen, and then I remembered I wore one in a play in high school, so including rehearsals and performances, 21-50 is probably more accurate. So I screwed the poll.
For awhile I ended up at a formal banquet or something about once a year, but like** corkboard**, a lot of my total came from high school plays.
And once I went to an ambassador’s reception!