[if anything] {adv. phr.} More likely; instead; rather. * /The weather […]

[if it's not one thing it's another] If a certain thing […]

[if need be] {adv. phr.} If the need arises. * /If […]

[if only] I wish. * /If only it would stop raining!/ […]

[if the hill will not come to Muhammad, Muhammad will go […]

[if the shoe fits, wear it] If what is said describes […]

[if worst comes to worst] If the worst thing happens that […]

[if you can't lick them, join them] If you cannot defeat […]

[IGAHP] "I've got a huge penis"

[IIRC] "If I recall correctly", or "if I remember correctly"