The verb 'faighinn' in the future tense.
Irregular verbs, don't you just love 'em? There aren't actually that many in Gaelic compared to some other languages, but there are a few there with the primary purpose of being a challenge to remember.
In order of 'stem - past tense - future tense,' my four nightmare verbs are:
rach - chaidh/cha deach - thèid (go)
abair/can - thuirt - canaidh (say)
faigh - fhuair/cha dh'fhuair - gheibh/chan fhaigh (get)
thoir - thug - bheir/cha toir (give)
I find it really hard to commit these forms to memory. 'I went' is 'Chaidh mi...' yet 'I didn't go' is 'Cha deach mi...', as irregular in Gaelic as it is in English. Then in the future form you get another word - thèid - but at least this is fairly consistent throughout, dropping its lenition when making pronounciation easier.
The best way to remember things, of course, is to get them to make you laugh.
My 'Caraid Cànan' M made me laugh the other day with the verb 'get' in the future tense, and finally it has stuck.
All through the future tense, it's 'faigh' (rhymes with 'high'), with or without lenition, except the simple future which is a completely different word: Gheibh, loosely pronounced 'yeahv'.
Now, if you've been learning Gaelic more than a couple of months you'll soon be told that the phrase 'mas e thu toil e' ('if you please') is never, EVER uttered by native Gaelic speakers in everyday use.
Manners are implied by use of tense and the question form, so while 'bheir sibh dhomh cupa tì' (give me a cup of tea) is as direct and rude as it sounds in English, the phrase 'am faigh mi cupa tì?' (may I get a cup of tea?) is normally used instead. Forget sounding American, 'am faigh mi...' was around for a long time before English-speaking folk started imitating their American cousins.
So... we're used to 'am faigh mi...', to which of course the response in the negative is 'chan fhaigh' (easy enough to remember) but in the positive is 'gheibh'. Gheibh, as already mentioned, bearing no resemblance to the root 'faigh'.
So... how to remember this?
A great way to remember this is to think of the non-Gaelic speaker visiting a Gaelic speaking canteen-style cafe, and trying their best with the people serving the food:
'Am faigh mi seo?' (May I get this?) 'Gheibh' (You may)
'Am faigh mi seo?' 'Gheibh'
'Am faigh mi seo?' 'Gheibh'
Perplexed, our non-Gaelic speaker takes his food to his table and quietly has a word with his Gaelic friend.
'Well, they're a cheery bunch in here' he says to his friend.
'What do you mean?'
'Well, every time I used that phrase you taught me to get something, they practically cheered! I thought they were going to high-5 me every time!'
'I still don't get what you mean.'
'When I asked for and pointed at the fish, they went 'YEAH!'. Then when I asked for peas, they went 'YEAH!!' Then when I asked for chips, they again went 'YEAH!!!' Are they always that happy?'
His friend thought briefly, then put his hand over his eyes: 'Gheibh' said the friend. 'Gheibh'.
Now, can anyone think up a joke for chaidh/cha deach/thèid? ;)