With a new game and a new clan there seems to be a load of invites flying around which, coz I'm polite I try to answer as soon as possible  To speed up replies, and to cut down on me dying so often, can I suggest a few abbreviations:-  PYUA - Pick you up after we finish this game  SFP - Sorry, in a full party, try again in a while  SOLO - I'm a bit moody today and want to play by myself 
  
TBNT - Thanks but not tonight  (you could use this if you're online playing with IRL friends) 
  
TROL - As Tam said, arsing around only invite me again if you're up for laffs 
  
FOOD - Sorry, going soon for grub, might be back on after   
ZZZZ - Thanks but finishing soon for the night  Make some suggestions and I'll add/amend the OP