Strange gig

I had a bad gig for the first time in years last night. I wanted to try out some rather under-prepared new material so (to be on the safe side) I opened with my 100% banker of an opener which always gets a great laugh.
Except last night.
Comedy pause. No laughs. Punchline #1. No laughs. Punchline #2. No laughs. I couldn't figure it out. Then I stumbled into some underdone material and managed to mumble my way through to a half-hearted round of applause at the end.
After the show, another comic came up to me and told me that 30 minutes earlier (while he was on stage and I was on my way to the gig) he had just done an almost identical joke.
The audience must have been thinking "Who is this English twat doing the same gag again? What an arsehole." Hence the uphill battle.
It’s the first time it has happened, and I'm actually surprised it hasn’t happened before. I've been doing that gag for six years, and the chance of no-one else thinking along the same lines is zero.
Having similar gags is not the problem. The annoying thing is that wasn’t able to judge the impact of the new gags because everyone thought I was a twat.
They might be right.