Every character of mine will now be Bard 6 (Satire). Damn it.
Also, being really anal, the Satire 3 feature can net you 5 or more proficiencies. The RAI is blatantly obvious (just 3), but technically it says, "If you are already proficient with thieves' tools or in Sleight of Hand, choose another skill proficiency for each proficiency you already have," not "for each of those proficiencies you already have." So if you have 3 (Bard), one of which is thieves' tools or Sleight of Hand, then you gain proficiency in the other of the two, one other skill, and then 3 more proficiencies since you already had 3.
If you had more (via race, background), then those would get you more proficiencies too. By this method you could probably be proficient in every skill in the game (18). Bard gives you 3 (Sleight of Hand and two others), a background gives you 2 (whichever), Variant Human gives 1 (any) plus a feat (Skilled), which nets you 3 more (any). Then Satire 3 nets you 1 (any), thieves' tools and then doubles your pre-existing number of skill proficiencies: (2 x ( 3+2+1+3 )) + 1 = ( 2 x 9 ) + 1 = 18 + 1 = 19. So you actually end up with an excess skill proficiency.
Note: this is absolutely clearly not RAI. RAI is "for each of those proficiencies you already have."
The amazing thing is that line isn't even needed, although the relevant rule is buried in an obscure place in the PHB. Rather than being in the section about skill proficiencies, this little tidbit is tucked into the Backgrounds section: "If a character would gain the same proficiency from two different sources, he or she can choose a different proficiency of the same kind (skill or tool) instead." While technically it would function very slightly different, the difference would go unnoticed by most players. Namely, as written for the Satire feature (assuming the RAW is adjusted to match the obvious RAI), you can trade a duplicate thieves' tools proficiency for a skill proficiency, whereas the base rule would make you trade it for a tool proficiency instead.