That certain SparklyCart also made clear that his/her post was completely in jest, and that they absolutely did not advocate endangering flight safety by carrying out such acts 'in real life'.
Whether the humour/'in jest' was appropriate or not is another question, but the OP has made it clear that he/she would absolutely not do such a thing.
I'm sure many of us will have said things in jest or humour which we'd never dream of doing.
If I seriously thought that one of my colleagues was likely to pull such a stunt as 'eye drops in coffee', I'd not only confront them about it, I'd put in the approriate 'heads up' to those who would need to investigate. However, in 8 years of flying, meeting and working with literally thousands of fellow crewmembers, there has only be one occasion where I've ever had to question a colleagues intergrity - and that wasn't at BA.
It'd be interesting to see some of the threads about BA Cabin Crew on the BALPA forum - there apparently is no shortage of pilots who seem to trawl through the private 'membership only' BASSA forums!