There are two different Party Jawas you can get in SWTOR:
The first is the original Party Jawa, released and given only to players that celebrated the release of SWTOR going Free to Play in 2012,
The second is the Celebration Jawa, which is the same as the Party Jawa however this Jawa can be bought from the Anniversary Vendor every SWTOR anniversary event and instead carries a Balloon with a big 5 on it.

Both Jawas are an inventory item that when used summon the Party Jawa to celebrate with you for 3 minutes (with a 5 minute cooldown). While active the Party Jawa will fly (yes fly) around your character and track kills you make bother against players in PvP and other Jawas you kill on Tatooine.

There is a Title and 3 total achievements you can earn by using the Party Jawa or killing other players partying with their own Party Jawa:
That’s Just Wrong! – Kill 100 Jawas on Tatooine while using the Party Jawa.
This one is really easy as an Imperial if you head directly to the North of Tatooine and kill the Jawa base above the Republic Taxi Zone.

Life of the Party – Kill 500 Players while you party with the Party Jawa.
This one takes the longest but is the easiest, as you can just use the Party Jawa while playing PvP Warzones and you shoul rack up 20-30 Party Jawa kills per match.

This Party’s Over – Kill 100 Players that were partying with the Party Jawa. Reward: Party Crasher Legacy Title.
Probably the hardest one, you need to kill players in the Open World or in PvP that are partying using their Party Jawa. This can be tough as not many people use the Party Jawa after the Anniversary Event ends.