"IRN BRU! Tapadh leat a bhalaich!"
Translation:IRN BRU! Thank you, boy!
It's called lenition. It's used to denote the vocative case, among other things. With masculine nouns beginning with a consonant (except L, N and R), you lenite the noun by adding an H after the first letter and an I after the last vowel. The sound also changes: BH sounds like V in English.