I seem to remember that it involves the word "observe", but I can neither recall it nor find it in a thesaurus.
Learn English – the expression for rules that are typically flouted
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Related Solutions
Cut to the chase.
Cut (or get or return) to the point (neutral if preceded by "let's" or "we should" instead of "you").
There is the term choking in psychology. It is performing worse under pressure or if you are expected to perform well. It is also mentioned that, if you are being watched when you are performing a task, it means that performing well in this task is important. Thus, people perform worse.
The term choking is usually used in sports but you can choke in social interactions or anywhere.
Below is an explanation of choking and an example from the book "The Curse of the Self : Self-Awareness, Egotism, and the Quality of Human Life" By Mark R. Leary Professor of Psychology Duke University (2004).
Social loafing is a related term also. It is not exactly about being watched but you perform less when you are in a group or if there are people around.
In the social psychology of groups, social loafing is the phenomenon of people exerting less effort to achieve a goal when they work in a group than when they work alone.
Best Answer
You are probably thinking of more honored in the breach than the observance, which can be found on phrases.org and on wiktionary under "honor in the breach":
Personally I find phrases.org's "real meaning" to be poorly phrased; it should say something like "the original intent of the phrase was to point out that it is more honorable to break certain rules than to obey them." The quote is from Hamlet, specifically when Hamlet was observing that it was customary for his stepfather to get all liquored up and engage in shenanigans. He then says