1) The characteristic of not being able to "tone down" one's personality. When a situation calls for a relaxed, collected, and in particular, calm manners, a person who is "too much" will show up after ten rounds of tequila-shots and make an excessive number ill-received jokes that s/he stole from Comedy Central Present's not being able to chill the fuck out; or 2) not being able to chill the fuck out
i.e., Philip is "too much" man, I can't fucking stand to be around him before noon, or after 8pm. I mean, he's cool when I'm drunk and shit, but other than that, why can't he relax.
i.e., Tell that kid to stop being too much, we're at my little brother's barmitzvah