Is it possible to feel any effects after chewing one coffee bean? The question title says it all: My colleague wanted to try my coffee, so he grabbed one bean of coffee (roasted) and chewed it up.

After several minutes, he claims, that it has positive effects on him (feels "juiced up)

Obviously, I am wondering now: Is it just placebo effect, or is there any possibility to feel this after chewing up only one bean?
First I want to draw a comparison between how much caffeine is in a coffee bean versus a cup of coffee, a cup of tea, or a double espresso.

In a standard cup of coffee, there is approximately 150 mg of caffeine. In a cup of black tea, steeped for 3 - 5 minutes there is approximately 50 mg of caffeine. In a double espresso there is approximately 60 - 90 mg of caffeine depending on the roast, grind, extraction time, etc.

In one dark roasted espresso bean there is approximately 6 mg of caffeine according to this source.

If a person is extremely sensitive to caffeine, they would probably be able to feel the effect of 6 mg of caffeine. However, if someone is a coffee drinker, the likelihood that this caffeine is actually affecting them is very unlikely.

If your friend never ingests soda, coffee, tea, or caffeine in any form then he may have felt some of the effects. In my opinion, the majority of the way your colleague was feeling was probably a placebo effect.

Edit: Coming back to this answer, I neglected to mention the effect of the taste of the coffee bean. Taste and aroma can powerfully affect and stimulate the brain. Due to the relatively strong taste resulting from chewing up a roasted coffee bean, this may have also contributed to the reported feeling of stimulation.